The order in which the approvers are listed in the channel dictates the order that the invoice will go.
Eg. this invoice will go to Brittney, then Neha, and finally Penny.
To change the order of your approvers:
Go to your approval channels settings.
Select the appropriate approval channel you wish to change so that the criteria and approvers are showing.
Select the edit button next to 'Approvers'.
Choose the approvers you want for the approval channel by selecting the checkbox next to their name and then the arrow in the middle of the dialog box to move them to the 'Selected Approvers' side.
You can change the order of the approvers by clicking their name and dragging it to the appropriate spot. The little black rectangle or red arrow will show you exactly where the name is being dragged.
You can create an "either/or" approval channel by dragging one name on top of another. This group approval means that either user can approve the invoice in order for the invoice to continue along workflow.
When you are done creating your approver list, select 'Save'.