[sunami88]

When you log into the Kobo webiste, login, and then click on "LIBRARY" near the top right.

This will bring you to the books you've purchased, and should let you download them as an ePUB. I say should because every time I click on a download link in Chrome it downloads a "URLLink.acsm" file. In a more supported browser your ePUB should just be saved to the hard drive.

Let me know if that works, I'm a noobie too :P .

EDIT:
Y'know what, even in the dreaded Internet Explorer it just downloads that file... Strange.

EDIT2:
Ah, thank you wallcraft haha.