An Expense administrator can change the Approval Route as below:
Click Settings, then click on the Expense users.
Search for and click Actions.
Select Edit.
From here find out and take note of what Approval type they are on.
After taking note of the approval type, go back to settings and click Approval.
In here select the approval type and click Actions.
Select Edit.
In this menu, the person's account should be linked under one of the Approvers, click the X to remove the user as an approver.
Once the user is removed, type in the name of the new approver and hit save.
Please note that this will only apply to claims submitted after the change, and existing claims will not be updated. To address this, you could grant the new approver permission to approve on behalf of one of the existing group members