In the the top left corner of your main guild layout is a little box where your logo will go... If you don't have a logo already up the following image will be on you page.
Why Do I Need A Logo?
A logo is a great way to make your guild look more profesional, better, unique, and even more fun!
How To
1) Right Click (if you have an Apple hold down the button) on the logo you want to use for your guild.
2) When the menu pops up select 'Save Picture As...' (or something that means the same thing).
3) A new window should pop up.
4) Make sure you know where your saving the picture (the folder, area of your computer). You may want to save it on the Desktop. To change the location of where your saving you need to find the area that says 'Save in:' and then select from there.
5) Go to your guild.
6) Under 'Admin' (on the left of your guild where all the links are located) click on 'Guild Layout'.
7) When the next page pops up click on 'Upload/Change Guild Logo'.