Hmm, more information needed I think!
First of all, are you able to work on your exams full-time, or do you have any other commitments?
Also, how long are you going to be in the USA for? Most of the exams will make much more sense once you've done a bit of flying, and you can see how things work in practice. I'm always a little worried when I hear about people doing the exams before they start flying, because I wonder if they're actually learning anything or just reciting answers to questions parrot-fashion.
Of course if you're cramming all of your flying into a very short time-scale, as many people do when they go abroad to do their PPL, it may be that you have no choice because you won't have time to study once you get out to the USA.
My advice would be, if you're going to have lots of spare time in the US, don't worry about the exams for now. If you're not going to have any time, then push on with the exams - you should be able to pass them all in that time comfortably if you're working on them full-time. If you're not sure, then why not get some of the exams out of the way - Air Law, Meteorology and Human Factors seem like good starting points. Others, like Aeroplane Technical, Navigation, and R/T I would think will be much easier later on, as long as you've got the time.
Good luck!
FFF
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