Hoe to remove the back panel and clean or replace the fan for MacBook (13-inch, Mid 2009)

I don't intend to offend you, but how do you know the laptop is overheating?

You can run the Apple Hardware Test to check the cooling system including the fan and temperature sensors.

A laptop which is running hotter than usual might just have an application or process which is running non-stop. You can check this using Activity Monitor located in the /Applications/Utilites folder. If the laptop is just shutting down, then there are a lot of other things which can cause the problem than a fan. You can run EtreCheck to check for software issues and post the report here using the "Additional Text" icon which looks like a piece of paper. Booting into Safe Mode is another way to discover software issues.

Sometimes an SMC reset and a PRAM reset can fix things (hold the PRAM reset for at least three chimes so it activates several times).

I just wanted to be sure since people get into a lot of trouble opening up their laptops for unnecessary reasons. If the fan and heatsink are clean and the fan is working, then perhaps the thermal heatsink compound has dried out and needs to be replaced.

Make sure to disconnect the power adapter before removing the bottom case. Immediately disconnect the battery once the bottom case is removed. Be careful as it is very easy to damage the fragile components on the circuit board and the fragile cables & connectors.

The information you seek can be found on iFixIt.com with their guides. There should be one for your laptop.