How to upload photo?

Let's say I'm on this forum with my Ipad, how can I change my avatar by upload some photo from Ipad?
it's like impossible
Thanks a lot for any advice

It's easy if you are using the app.
Click on profile then click on your avatar, you are then given he option to upload a photo / picture.

Thanks for your advice,

however I mean in general cases, I don't prefer to install all apps of all forum I join, and in some cases, forums/sites don't have app to install on Ipad

You could find an alternative browser such as iCab which will allow uploads, or you could send the avatar picture to a friendly moderator who can change the avatar for you.

Go to your profile - edit profile - change avatar you will get image upload option.