Can I make my bootcamp partition bigger without formatting it?
Not with the built in tools. Moving the start of a partition is no trivial task. Resizing your main Mac partition only grows/shrinks it, but because your bootcamp partition resides further on your disk, it needs to be moved up before it can be grown. This is not a trivial operation and is not supported out of the box in either OS X or Windows.

You will need a specialised 3rd party tool like iPartition, but use with care and triple check compatibility.