SQL: Cannot delete SQL Login account

Issue:
Cannot delete SQL Login account

Other symptoms:
It says that the account to be deleted is in use

Resolution:
Disable login first before deleting. Steps are as follows:

1. Go to Security > Logins > Right click the account to be deleted > Click on Properties
2. In the Login properties window, click on Status
3. Under Settings > Login, select 'Disabled' and click OK

Afterwards, try to delete the SQL Server Login account again