did you have DFP 1 installed before?
Do you have Universal Email 4 installed?
Universal Email 4 includes the file upload of DFP.
If you have universal Email 4 installed, you should uninstall it, then uninstall DFP 2 then reinstall UE4.
to add file upload with UE4, go to Insert -> Web Assist -> File Manipulation.
The fit to width option will auto calculate the height based on the width, this is why you cannot set it.
if you wish to set both height and width manually, select the the fixed width and height option.