Shimano chainring / crankset compatibility
The answer is yes you could replace your crank set with the FC-2303 but you would have to change your bottom bracket also. Look up the Shimano tech docs for these cranksets, all the information you need is there as well as the steps you take to change the bottom bracket.

The triple ring crankset is the FC-3304 with a 45mm chain line using a 118mm octalink bottom bracket.

The FC-2303 is the triple ring crankset which also has a 45mm chain line but uses a 113mm square taper bottom bracket.

So alongside the crank extractor you will need a bottom bracket tool. I got a crank extractor and a BB tool for about $10 NZD each. To change a rear cassette you will need a lock ring nut which will fit your rear cassette.

I shop at Chain Reaction Cycles which ships from the UK and is cheap and reliable with fast shipping. They sell components and tools at good rates with ok shipping rates.