Approvals can be managed under Time > Approval Requests by Administrators or by Consultants with the Approver setting.
It's important to note that removing an approval is final - it's not possible to reinstate an approval once it's removed. Instead, you would need to resend the request email to the Contact from the Pending tab, or completely delete the Pending approval (as shown below) then re-request approval.
If you have an approval that needs to be removed, simply navigate to the Complete tab, open the approval, and click the x to remove the approval.
Removing a Complete approval will simply move the approval request back to Pending, setting the time entries as Pending Approval. If you wish to remove the approval request altogether, then from the Pending tab you can click Delete Request to completely remove the request.
Once the request has been deleted any time that was included in the request will be marked as Timesheets Pending. The time can then be edited or deleted as required, and approval can be re-requested.