HI Mick,
I'd say it unscrews unless it has been bonded on as it a 3.25" to 2" adapter,
likely the same screw on adapter
as shown here . I would try a suitably sized oil filter wrench with some PVC tape wrapped around the adapter outer surface to protect it from any possible marring or slip. I would suggest one of these REPCO branch wrenches, probably the
GV051 87-95mm wrench, but possibly the smaller (doubt it)
GV052 73-83mm wrench. Unfortunately Aluminium has a tendency to gall (stick) in screwed and fine tolerance joints. Sometimes a light coat of vaseline on the threads can help future unscrewing of the joint or some anti-seize/gall compound can be used if you wish.
Anyway
make sure you measure your adapter outer diameter to be certain, but since the 3.25 inch (~82.5mm) probably refers to the female thread pitch diameter or the female thread major diameter then the required size will be a few mm extra to account for the wall thickness of the adapter and probably, although not certainly, necessitate the GV051 87-95mm Oil Filter Wrench.
TRy before you buy.
Best
JA