Well, as iFixit doesn't really offer services, I'll try to walk you through this in as clear a manner as I can.
First of all, it's helpful to do this in the day time- then you can see what you're doing.
# Turn off the light
# Wait a minute for the bulb to cool down
# Look at the number that is on the top of the bulb- it's probably something like 40W or 60W
# Make sure you have the proper replacement- I would suggest not going above a 60W bulb
# Gently unscrew the dead bulb. Make sure you work in a straight pattern, so as you can get the bulb out with minimal hassle
# DON'T TOUCH THE INSIDE OF THE SOCKET!!!
# Get your replacement bulb and carefully screw it into the socket. You'll know you've screwed it in far enough when it is firm, but not unmovable.
# Flip the switch. If you worked carefully, you should have a working light again.
Enjoy!