how to change slider and carousel photos?

hi,im new to opencart,i began to administrate an e-shop,heres the site www.sofiadis.com.gr
i would like to ask how to change photos of the homepage.not products(i already do that).
please if there is any step by step guide how to do that it could be very helpful,i apologize for my english.
also,how to change banners.

Take a look at following discussion thread. You may find possible answer for your query.
http://forum.opencart.com/viewtopic.php?t=57913