I have now a Xbox X360 with a 20GB HD and it is almost full.  I wonder if I can replace it with a 120 GB HD and can I put all my DLC on a USB stick and so replace it on my 120 GB HD (otherwise I have to download it all again and will my download limit die) and can I put savefiles on a USB stick aswell? 

I downloaded more than 100 things already and I really don't want to download them all again (can't even remember all the stuff) and ofcourse don't want to lose my savefiles aswell.

I hope this helps, though I'm not sure if they ship to China...:

http://www.xbox.com/en-US/support/systemuse/xbox360/console/datamigration.htm

Also, I don't think the memory stick thing will work, but I could be wrong.

Damned it is complicated, I guess I better go to a store right?

When you buy the 120GB Xbox Hard drive it comes with a data transfer cable.

Thanks to let me know.  I am going to the store and ask if they can do it.  I really don't  think it is a good idea to do it myself =p.

It's actually a lot easier than it sounds. You pop in the CD and it gives you step by step instructions. My brother-in-law did this himself and he's very computer illiterate

Best Buy charges like, $50 to do this, so it'd probably be better for you if you tried it on your own, save you some money...