More information would help us to answer you better. Is it a manufactured computer or custom built? What type of CPU, motherboard, etc.?
Just off the top of my head:
- Remove wires over the fan and heat sink to improve air flow.
- Add more fans to bring more cool air in the case.
- Blow out the dust from the computer, with a compressed can of air or a air compressor if you have access to one.
- Change your heat sink and fan, stock heat sinks are not that great.
- Buy a better case with more fan options.
- Remove the heat skin and fan, verify its properly installed.
- Use a better thermal pasted.
- Power supply sometime give off a ton of heat, upgrade to a more efficient one. If your power supply is hot to the touch it could be the problem.