Why can't you? What exactly happens when you try?
I dont know if im doing the right thing.
When i start a new project i clic on new sequence and a bunch of presets appear but the 720p options hav a 1,33 pixel option and i can't change that.
Ohhhhh.... i found it!! I was doing so worng!! It's just select on Settings > Editing Mode: Custom!
Thanks dude! You helped me a lot!