To remove an identified user, click on the Remove button alongside their details in the list. Then confirm the removal by clicking the subsequently displayed Remove button to deactivate them. A message will be displayed confirming that the user has been removed. This has the same effect as someone deactivating the product on their computer.
If the license is being used the customer portal will still show you 0 users available and by removing the user you will free up the activation.
The number of users you see displayed in the customer portal can be different to the number of activations available on the license. The number of users displayed in the portal is fixed. If you have a 1 user license, you are only entitled to 1 user and the portal will only ever show an entitlement of 1 user.
But a license often has more activations than the user allocation as over time activations may have been added due to system crashes or for the user to activate their license on another machine, such as a laptop.