We don't allow delete/removing a client as it may compromise a user's system.
You can just ARCHIVE your client.
Please note that you should have an access to archive a client. Please refer to this guide to know - Team Access
Two ways to Archive
Search the client via top left.
Then press the button "Archive"
Go to "CLIENTS" via top right
Tick the box next to the client you want to delete.
How to see the list of the Archived client?
Click "Archived" Tab
Click the arrow if you want to make your client in Active mode again.