Enlarging the bore of an existing flute is tricky. Is this a conical bore instrument? If so, you'll need to make a larger tapered reamer. Then you are faced with holding the work while you re-ream it, and you have to be careful that you don't accidentally crack the body of the flute. Same is true for a cylindrical bore flute, actually, in terms of re-drilling it. And making a larger bore on a finished flute means that now the wall thickness is reduced, which will have an effect on the tuning.
Making the finger holes larger is a
fairly easy way to give a bigger sound, but of course you sharpen the notes. If you don't have "tuning holes" (i.e. you have an integral foot) then you might have to cut a bit off the end to compensate for the tuning changes brought about by enlarging the holes.
If the embouchure hole is already a good size then you may not want to mess with it. Trying to get a bigger sound by enlarging it is probably not a good strategy, IMHO. It might have some small effect, but you risk messing with the voice of the instrument.
To do something like this effectively, there is certainly some strategy and engineering involved, and if you've never done such modifications before you might very well ruin a perfectly good flute! Even if you succeed in making it louder, it doesn't follow that the sound quality will be better, or even as good. Might be a change for the worse! Or you might totally nail it. If it's just an experiment and you aren't attached to the flute it could be educational. If you like this flute, I'd leave it alone and see about acquiring a louder flute