You can rename accounts via your Blockstream Green desktop application. The changes you make will be reflected across all other devices that have access to the respective accounts.
Note: Make sure you understand the difference between wallets and accounts.
On your wallet's home screen, select the account you want to rename.
Note: You can rename every account except for your main account (the default account that comes with your wallet).
Click on the account name.
Your account name is now updated.