I don't touch online due to the fact it's VAC protected etc. If you want to risk it then it shouldn't be too hard but if you don't know what your doing the easiest method would probably be searching for XP and modifying that, I personally haven't touched online as I have no intention on playing it.
If you really want to find it, then find the value of the XP, get a working pointer and look in the memory 'around that area'. With enough motivation and effort you'll find it. Highly recommend a second account though if you plan on messing with online stats etc, currently £10 on G2A I believe.