Unless you put the maximum RAM in your Mac when you bought it, chances are you can add more, which is what we're going to help you do.
Remember, new memory is an affordable way to get your Mac running faster. Depending on what Mac you've got, you may need to take out the existing RAM to put more in, so bear this in mind when you're buying. If your MacBook Pro already has two 1GB chips (one in each slot) and you want to upgrade to 4GB, you can't simply buy an additional 2GB. Check System Profiler for what you've got now.
The best place to get memory from is Crucial, which has a simple guide to ensure you buy the right RAM for your Mac.
To prevent static charge damaging your equipment, ground yourself before you begin by touching something metal. Unplug all power sources before you open things up. Get an anti-static wristband from an electronics shop for peace of mind.
When handling RAM, hold it by the edges and don't touch the gold connectors. And remember that components may be hot if the Mac's been running recently!
How to upgrade the RAM in your MacBook (late 2009 model and later)
1. Open up your MacBook
Undo the eight screws on the underside of your MacBook and lift off the back case – gently pull free the clips at either end. Two RAM chips are in the middle on the right-hand side one above the other; remove one or both.
2. Take the chips out
Find the clips at either end of the existing RAM stick and press these outwards with your thumbs. The chip will pop up so that you can grip it at either end. Gently slide the chip away in the direction it's pointing.
3. Pop in the new memory
Line up the connectors of the new RAM with the RAM slot – it'll only fit one way round. Gently push it in at the angle you removed the old one. Press the upper end down to clip it into place. Then put the case back on and reboot!
How to put more RAM in a MacBook Pro (2009 model and later)
1. Open your MacBook Pro
With the screwdriver, take out the screws from the back plate – they're not all the same length, so note where each came from. The two RAM slots are located fairly centrally, one above the other.
2. Out with the old…
At either end of the existing RAM, press the clips outwards with your thumbs. It should pop up at a slight angle. Grip it at either end and slide it out in the direction it's pointing. If it doesn't come away, check the clips are undone.
3. …In with the new
Get your new RAM and line the gold connectors up with the slot. Press it in at the same angle the old sticks came out at, then push the upper edge down to clip it in place. When you're done, screw the case back on.