Only Account Owner users have the required level of access to remove other users from your company account or change their permission level.
Here's some quick and easy steps to remove a specific user -
Head to the 'Company' tab from the main menu
From the dropdown, head to 'Settings'
Go to User Access in the top menu
On the user you need to make changes for (whether that be adjusting the access level or removing them altogether), click More.
You'll see the option to either Change Permissions or Delete them altogether from the drop down menu. If you're just wanting adjust their permission level, click Change Permissions.
In the next window, select a new role for the user and Update.