You would first want to go to http://www.mediafire.com
Click on drag files here to start uploading
Click on the + and on the very top you'll see a address bar, type in %appdata%/.minecraft/saves
You should see the save you want, right click that one and click on send to then compressed zip folder and double click on the compressed folder when it's done
Click begin upload, once it is done you'll see copy link, do that
Go here http://www.planetminecraft.com/account/ ... /item/new/ and fill out the forms then at the very bottom you'll see World download URL, you put the mediafire link there that you copied.

If this doesn't work, please tell me the operating system you have

To change a map in creative, you could make it a server then op your self and use /gamemode mcign 1

If you can't run a server try this video http://www.youtube.com/watch?v=3UvluCAvivc