Go to the Contacts tab and select the contact you would like to add as a user.
Check if you have enough user licenses purchased. If no, please upgrade your account to get an intended number of users.
Click the Convert icon from the top or right-click menu and confirm the conversion.
After the confirmation, the user with the assigned Pro user class appears in the list on the Administration and Contacts tabs.
It is currently not allowed to select what class of users you would like to assign during the conversion. This feature will be implemented in one of our future releases.
Your newly created user will use your account quota that you can change on the Administration tab while editing this user.