Ranjan, yes you can. There won't be any damage to you UPS. But check your UPS battery does it has REALLY 12v inbuilt battery. Everything that can damage your UPS is other voltage and not ah.

I know this is a late reply, but as long as the battery is the correct Voltage you can change the Amp Hours to what you require and no damage would occur. The only thing you need to remember is the UPS will be limited to how many ah the UPS itself can recharge . For example if the UPS is fitted with 7ah and you change this to 100ah, then the battery will probably never recharge after a full discharge.

I hope this helps.

There are very good UPS Batteries that are quite cheap available to buy here -

Good luck