In the lower left corner of your posts you will see your name, a date and time, and then the word "Edit." If you click on the word "Edit" you can then change that post. To change images you need to click on the "More options..." button after you go into edit mode.
To add a new image, you can either save and re-upload a copy of the image I posted or you can incorporate the image that is part of my post. To do the latter, click on the "Media" icon
View attachment 1048766 in the toolbar while you're in "More options" and then paste the link
http://www.audiokarma.org/forums/index.php?attachments/img_1495edit-jpg.1048711/
into the box where it says "Enter media URL".
You could also just put a note telling people to look at the image in post #33 (my post) and leave it at that.
To delete your original image use the "Delete" button next to the image as listed in the "Attached files" list (from within "More options").
I guess some of the above might be a little different for you if you are using a phone/tablet instead of a laptop/destop. When you have what you want, don't forget to click the "Save changes" button. If you use the browser back button from within "More options" your changes will be lost.