UPS

Decrease the amount of power required out of it.

I think you should analyze the system yourself and come to your own conclusions. We may not be around next semester.

Increase the frequency.

As your post gives no reasoning behind such a rather unusual request, gives no explanation, no figures, no numbers, no values... all you speak about is reducing transformer size. Period. Well, padupoi, the solution is very simple. Just kick out your offending transformer and put in a smaller one. They cost less, too.

These people http://www.capturedlightning.com/ shrink metal coins. The process would probably work on transformers too.

But a smaller transformer and replace it ... That how..... See so Simple.... No need to thank me...

u need to use a better quality winding and core material u can havea forced air cooling by a fan so a smaller xformer will take the load

Physically , changing a small transformer. Remove the cover panels of UPS. disconnect all wires connected to transformer. Remove all fixing screws/bolts of Transformer and take it out. Fix the new reduced size transformer. Dont ask me whether it will work or not.