You can change an approver in Access Expense as follows.
Log in as an admin.
Select the Expense database that the users are linked to.
Click Settings.
Click the Expense users.
Click Actions, Edit.
Note the approval type the user is on.
Go back and click Settings, Approval.
Select the approval type.
Click Actions, Edit.
The person's account should be linked under one of the approvers. Click X to remove the user as an approver.
Type the name of the new approver.
Click Save.