It's probably your CPU ventilation clogged with dust. Many machines have user-serviceable fans. For example my Dell has a little Philips screw which, if you take it out, allows the CPU fan housing to slide out, and makes it possible to clean it. First time I did that my average CPU temperature dropped from 80C to 37C!
Check the documentation which came with your laptop, or look on the manufacturers website. Dell are excellent for this - you can download the technicians handbooks which describe with excellent diagrams how to disassemble machines. Way cool. See here for example