Another Rsync question

I develop my own simple websites. When you test different designs many times f.ex not used pictures stay on the webserver. Now I have a website where there is a lot of not necessary files on the server. I want to use rsync to delete all files on the webserver that is not on the source
Becuse I am not sure how to do it I hope someone can write down the string. I connect to the webserver using ssh with a keypair