When you say "try" racing, you mean you actually think you can compete? Or you just want to enter a few races?
If you really want to compete, you've got 2 options... Neither are cheap!
1. Spend a fortune lightening your bike, being ruthless about weight everywhere. Go for very light wheels, super fast tyres, Carbon bars/post, razor for a saddle, 4ti eggbeaters, silly light brakes etc. And still end up with a bike that's 2lb overweight cos you're riding a steel frame, not a carbon one...
2. Buy new bike, specifically for XC racing!
Or... If you're happy just to have a go, not bothered about being competitive, just would like to give yourself the best advantage you can without spending too much money... Lighter tyres (Nobby Nics, Racing Ralph for example) should be port of call number 1. Swap the platform SPD's for a much lighter version as next step. Then step 3, go tubeless if you haven't already...
The 3 steps above won't cost more than about £100 all in, should save you 2lb in weight easily, and all of it rotating weight. You can then, should you want to, start messing about with lighter components here and there, and some lighter wheels if you fancy it, but I'd not bother to be honest... For £100 you can save 2lb in rotating weight, and that will have a marked effect!