Help needed - replacing chainset

I would be very grateful for some advice on my 1975 Holdsworth. It is currently a 5 speed and i am replacing the chainset to Campy Strada which has 2 chain rings. I have tried to remove the rear chainring but the bolts are not moving. i am just using an allen key but they are not budging at all.

My questions are:

1) I would have thought it should not be a problem to replace (providing I can get the bolts off)? Should i just have gone for a single chainring?

2) What can I do about removing the bolts?

3) It is a 52t which is larger than my exisiting one (not sure how big but it is smaller). what are the differences that I can expect?

Sorry about the basic questions as I have never touched my chainrings before.

Cheers

My message was lost. Do the bolts not move at all, not even with extra leverage?

The gear ratio won't increase that much.

The bolts are completely stuck annoyingly. The to be in chainset appears to be in very good condition. I'll keep trying but they are tough. i am just using an Allen key.

this video shows the basic tools and techniques > http://www.ehow.com/video_2360964_remove-mountain-bike-chain-rings.html

A pipe or even an adjustable spanner may offer you additional leverage to remove the bolts.

cheers! I tried fitting something on to the Allen key to increase leverage and they came off! Realised I needed some washers and a crank puller tool now so basically giving up and taking it to the bike shop for them to do it! :( I need better tools!!

^^ you'll get this for a few years/months struggling around with improvised tools, but bikes despite their lack of parts compared to say, a full size car, they need a lot of specialised tools.
eventually you'll start collecting tools, lots of them!