You haven't really made it clear what you want to do...I will explain why.
You started by saying that someone sets the priorities, and that they can move an order from priority 3 to 1 (for example) and this should make the other orders shift down the queue.
Then you provided an example where you set an order to priority 1 (we don't know what priority it was before) but you do not require the other orders to shift down (alter priority)...
This is contradictory without further detail.
If the supervisor makes an order move from priority 3 to 1 and there are already some orders at priority 1, where in the queue does it go? Perhaps she has the option to jump to the top of a priority group and bump the existing orders of that priority and below "down one level"? Perhaps she also has the option to merge with an existing group thereby causing no bump?
Also, please provide table creation scripts and sample data to help others to help you.
See this article for details of how to do this : http://www.sqlservercentral.com/articles/Best+Practices/61537
MM
select geometry::STGeomFromWKB(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