Hi oxbob, welcome to the forums. We are a helpful bunch, and I hope you will enjoy your time with us. Now back to your question. I don't have an iPad mini, but I expect the apps with both iPad and the mini work the same.
I'm guessing that you would like to use a photo for your Avatar. I change my avatar from the iPad forum app. I attach a screen shot which shows the stage at which you are ready to use a photo as your avatar. To get here, tap the profile button at the bottom of the screen. Tap inside the image box (your's is a grey and White silhouette at present). Chose insert from photo library in the prompt box. Pick the photo you wish to use and confirm. Go back to the posts page. That's it..
If you wish to update your avatar from the forums.net site, then go to your details. Tap settings in the strip menu towards the top of the window. The, select change avatar from the sub menu and follow the steps.
There is lots of good advice and info on here plus plenty of members all too willing to help with any problems.
Remember, search is your friend. If you can't find the answer you need and you post a question then give as much info as you can to help members help you i.e. iPad 1 or 2, etc. and iOS version and name of app if the problem is with a specific app........and please don't forget to read the forum rules http://www.ipadforums.net/forum-rules-help-info/2119-forum-rules-everybody-please-read.html
If you have other Apple products or are interested in other Apple kit then why not join our sister forum too at http://www.appleforums.net/ and for iPhone users, come and join in the discussion over at http://www.iphoneforums.net