If I expense the new one because it is less than $2,500 with the safe harbor can't identify if I delete previous alliance, give them the balance of the amount not depreciated, or let it continue depreciating until it finishes.
These two issues stand separately.
The old appliance is either still in use, or was removed from service. Deal with it as such. It won't keep depreciating, if it is out of service. You remove basis, you recapture depreciation, you deal with any money made from its sale or cost for disposal, and the difference is the gain or loss on the disposal of that asset.
Then, you deal with the new activity.
"Level Up" is a gaming function, not a real life function.