Yes there is a simple way.
As I remember when you're done with upploading and saving then you can simply grab the portfolio item and move it up-down.
Bring mouse to the portfolio item, left press and hold and move up/down.
Somewhat OT, thanks to @Upwork! After a lot of random disruption of portfolio item order last spring, the order was finally stabilized—except that until recently, the order in mobile web view was the reverse of that in desktop web view. This has been fixed, and portfolio items now display in the same order in both views.
I was about to post the same question. Issue I encountered was that the up/down arrows do not seem to be available on a consistent basis. Sort of here for 15 minutes then gone for who knows how long ......
What is the secret other than deleting tons of old stuff?