There's a size guide for that one - there's a link towards the bottom of the page. All the sizes are on the same file for that one, so just add it to your basket and then checkout (in this case without paying any money!)
They will then either immediately give you a link to download the file, or email it to you. Open the file in Acrobat Reader (other pdf readers are available, but Acrobat is good) - if you're printing it yourself you want the A4 file.
This file has layers, so you can hide all the sizes other than yours if you want to (if you want to do this and can't see how we can talk you through it).
Then print it, making sure that you're printing it as 'actual size' or 100%.
There will probably be instructions for assembly in the file, but if not Fran wrote an excellent tutorial
here.
(This is the tutorial
@wrenkins has linked to!)