I'm not familiar with the programme your using to edit the pictures but usually on these programmes theres a resize option. I use a programme called Picnik which is free to download, super easy to use and really quick photo editing, resizing etc. Once I'm happy with the finished picture I upload the pic to photobucket and then to the one ring.
I think you can also resize in photobucket if you wanted to stick with the editing programme you are using
Sorry I can't be more help but get it sussed .. lookin forward to seeing some of your work