You can only remove imported accounts and external accounts that you imported with a private key or JSON file (such as a hardware wallet).
Navigate to your accounts by clicking the account selector at the top of the screen. Here you will see any accounts you've imported, as they should be labelled.
In the account selector dropdown, click on the three vertical dots menu to the right of the imported account. This will open the menu where you can click 'Remove account':
In wallet view, tap on your account name to bring up the account selector screen. It doesn't matter which account you currently have selected.
On this screen, scroll until you find the imported account you want to remove. They should be easily identifiable through the 'Imported' label next to them.
Long press on the account to bring up the option to remove it. It'll immediately disappear from your MetaMask when you confirm.
How do I remove created accounts?
It is currently impossible to remove created accounts — the ones that appear as 'Account 2' etc. when you click 'Add account'. If you need to remove them, you must remove MetaMask from your device (Extension or Mobile), reinstall, and then restore using your Secret Recovery Phrase. However, DO NOT do this if you don't have your Secret Recovery Phrase. Without it, you won't be able to get access to your wallet when you reinstall. If you do this, bear in mind:
- This will not delete the account, but just stop it being visible in MetaMask: once created, your address is permanently on the blockchain and cannot be removed.
- When you restore using your Secret Recovery Phrase, MetaMask will automatically re-add previously created accounts if they hold ETH. See here for more information. If the account has some ETH in it, it will reappear when you restore.
- Any imported accounts and/or hardware wallets will also be permanently removed. Make sure you have their private keys/seed phrases (or Secret Recovery Phrase if another MetaMask account) backed up, or you won't be able to access them again. After you restore your wallet, you can re-add external accounts by importing them again.