Same as above, remove the heatsink and fan unit and clean any excess thermal paste off. You can use rubbing alcohol or something similar for this. Don't use anything oil-based though. Apply a very thin layer of thermal paste to the base of the heatsink as too much will also cause high temps. When you fit the heatsink make sure you have a good solid contact with the CPU and that ALL of the clips lock into place. It's best to work on opposite corners - to one corner and then the opposite corner as opposed to going around them in turn. You can google for more info on how to apply thermal paste if you want to.
Also make sure that your case has good airflow through it. Ensure there is no dust as dust is a very good thermal insulator. A can of compressed air is very handy for this job. Also try to tidy up your cable runs so they don't get in the way of airflow (and it just looks nice). The general idea is to have an intake fan at the bottom and an exhaust fan at the top. This is all down to the way air rises when it is heated. With this setup, cold air from the bottom is sucked into the case and then as this air is heated up and rises it is exhausted through th fan at the top. This general technique will often give you good results but obviously bigger or better performing fans or just more fans in general will help keep your system cool. Just out of interest, what case are you using? Good luck!