Just seen on another post by you that this may be a 2011 model.
Apple class products
discontinued more than 7 years ago as 'obsolete', and probably won't touch them because if they cause any damage they won't have access to parts to repair.
The MacBook Pro (15-inch, Early 2011) is right on the edge and is
classed as both 'obsolete' and 'vintage' (make up your mind Apple!) and the 'late 2011' is still classed as 'vintage' so it's uncertain whether they would service it - if you live near an Apple store there's no harm in asking.
However, if it's a 2011 model it's extremely easy to take the back off and give it a clean out with a soft brush and air blower. You just need a standard Phillips #00 screwdriver. Be careful there are two lengths of screws so you need to keep track of which screw goes into which hole (good guide
here). I would absolutely recommend doing this, if you're careful, as removing dust and fluff can have a significantly positive affect.
As for replacing thermal paste, it's a more
involved process and I would advise getting an experienced person to do it (if you're confident, careful and methodical you could do it yourself, otherwise...).