Okay so you go on the site and down at the bottom of the homepage there is a contact thing and it says you can email email@example.com.
email that address and tell them that:
!) you would like to make a custom hoody
2) Give them the size/ colors you want
3) tell them Ianj sent you.
"It's easy to dwell on the negative, but you have to be a bigger man to really take a negative situation and gain the positive" CR Johnson (RIP)