Firstly you will be limited in the time period you can edit any post so need to do it before hitting submit or quite soon after.
In the editing or reply windows just click on the photo you want to remove which puts a box around it and then press your delete button. To add a new photo just put your cursor where you want teh photo and click the little camera icon as you normally would.
PM me if there is one in a post thats now run out of editing time and I'll see what I can do. Done it for you.
J
Edited By JasonB on 12/03/2014 07:42:34