Whether adding or removing a user from the cloud environment (Online) you will need to raise a case online and reference this article.
You will need to supply what action you require:
To add a new user, you will need to supply the following information
Are they a new user or additional user that requires a new license
Please include the name of a user that should be removed
Client number
Name (first and last)
Email Address
Job Title
Phone Number
To remove a user, you will need to supply the following information
Please include the name of a user that should be removed
Name (first and last)
Email Address
Job Title
Phone Number
Reason