hey :)
atm im setting myself 10lbs a month, so its basically the same as your goal.
alls im doing is changing my eating patterns, so im cutting out any un-healthy stuff like chocolate or crisps etc.
im eating more fruit and veg and salads, just find the healthy stuff you like!
im also going the gym 3 times a week at least to get my fitness up.
if you cant afford the gym then go jogging and do sit ups or long walks or stuff like that?
hope this helps :)

if you want 20 lbs in just 2 months,
you have to work out a lot,
i do at leat 100 sit ups everyday,
and i know that sounds like a lot, but if you put it in little 10 sections, and take a breather and get a drink between them its alright, and the more you do them, the better you get and the easier it is to do them, and then you can add leg lifts and other work outs for your legs,

but the MOST important thing to do for weight loss is cardio, like running, and jumping jacks, , and dancing, and anything that gets your heart pumping a lot,

as for the diet, i recommend you should cut out sodas, and drink as much water as you can, you don't have to live like this forever but it's the fastest way for me, (:

Weight watchers..my first month i lost a little under 10 pounds.