When to use it

Sign out everywhere ends your Relic session on every device at once. Use it when a device is out of your hands and you cannot reach it to sign it out yourself:

A phone or laptop lost or stolen.
A computer you signed in on at work, at a friend's, or in a library, and then walked away from.
Any time you suspect somebody else has your account password.

Removing a single device from your Devices list ends up doing the same thing. The service that handles sign-in can only end every session at once, so taking one device off the list signs the whole account out. The Security screen's button is the one that says so before you press it.

Signing out everywhere

The button lives in Settings › Sync and account › Security, near the bottom of the screen, marked in red. Its line reads:

Open Security
Go to Settings›Sync and account›Security. On a phone the same Security screen sits in the settings sheet.
Press Sign out everywhere
Relic asks before doing anything, and the dialog says plainly what happens to which device.
A confirmation dialog headed Sign out everywhere? The body explains that every device signs out, that other devices lose access right away, that this device stays connected until its session next refreshes, and that your vault and recovery kit are unaffected. Below are a Cancel button and a red Sign out all button. The confirmation. Sign out all is the red one.
Press Sign out all
Relic answers Signed out on all devices. Every other device is out from that moment.
Choose what this device does
A second dialog headed Signed out everywhere asks Also disconnect this device now? with Disconnect and Not now. Press Disconnect and this device signs out too, and lands back on the sign-in screen. Press Not now and Relic tells you what to expect: This device will lose sync within about an hour. Disconnect and sign in again when ready.

The delay on this device is the only loose end. Every other device is cut off straight away; the one you pressed the button on runs on its current session until that session next renews, which is roughly an hour. Pressing Disconnect closes that hour.

Your vault is untouched

Signing out is about your account, and it does not touch your data. Nothing is deleted, anywhere.

Your items stay on the server, still sealed.
Your vault passphrase is unchanged, and your recovery kit still works.
The history already on each device stays on that device. A lost phone still holds whatever it had synced.
You sign back in with the same email and account password, and unlock with the same vault passphrase.

Because a signed-out device keeps the items it already had, this is the right move for a lost device but not a way to wipe one. If the device itself is a worry, use the phone or laptop's own remote wipe as well.

Removing a device from your Devices list signs the account out everywhere as well, so expect to sign back in on your other devices afterwards. The pane itself is covered in Settings: Sync and account.

Changing your account email

The same Security screen has Change account email. Its line reads Your login email. We confirm on both addresses. Your vault passphrase is separate. Open it, type the new address into New account email, and press Send confirmation links.

Relic then tells you what has to happen next:

Until you have opened both links, your old address is still the one that signs you in. Changing the email does not touch your vault passphrase, your recovery kit, or a single item. If you have already lost access to the old address, the change cannot complete, so write to support@relic.space instead.

Deleting your account

At the very bottom of the Security screen, in red and set apart by a gap, is Delete account.

Pressing it opens a dialog headed Delete account?:

Under that it says Type your email to confirm: with a box. The red Delete account button only becomes pressable once what you typed matches the address you are signed in with. Capitals do not matter. On iPhone and iPad the dialog leaves off the last sentence, because plans are not managed inside the app there.

Two things to know before you press it:

Your devices keep what they have. Deleting the account clears the server side. The history and the Vault on each computer and phone are still there. Export the vault first if you want a copy you can read, or take an encrypted backup file if you would rather it stayed sealed.
Cancel a paid plan first. The dialog says so, and it is easier than sorting it out afterwards.

There is no undo. Once the server side is gone, your recovery kit has nothing left to open, and the kit cannot bring back items that no longer exist. Export or back up first if there is anything you want to keep.