^ without opening it you cannot replace the thermal paste and you really cant do anything more than vacuum the exhaust event or blowing compressed air into it

is the warranty done if i got in 2007?

the warranty only lasts 1 year

it's best you watch gilksy's ylod guide on youtube (here is part 1 of 6) - after that you can decide for yourself whether or not you want to open it (it's not that easy to get to the cooler/fan)

I think if you feel confident enough you should do it and replace the thermal paste with the Arctic Cooling MX-2 (it's easy to apply/remove, cheap, non-conductive and a high quality paste)

^ This.

I did it last week and the console improved in terms of cooling and noise.

PS: Keep attention to the screws and their positions ^^. It's easy, don't worry. You need a Torx 5 or 6 to open it.