How can I customise existing access levels?

You can make changes to existing access levels by going to Settings->User Permissions & Access Levels. Choose the access level e.g. Administrator and click edit button. Customise the user permission settings attached to the role. Click Save.

For example, Manager wants to have access to the Reports. Admin can simply go to Settings-> User Permissions and Access Levels  -> click the edit button for Manager -> See Reports under System Modules -> tick and save.