i work on electronic equipment (tv's, dvd ,cd, and so on) and we get people all the time checking the fuse in their TV's. they see the fuse blown so they put in the same size, blows again. lets say they had a 4amp in there and then they put a 10amp. now the set comes on only because that bigger fuse takes longer to blow then the 4amp. in the time that it takes the 10 amp to blow other things are being burnt up due to the fact that the set is only rated for a 4amp, which is intended to blow quicker so less damage would be done to the set. this would cause more problems for you down the line if you put in a bigger fuse. if you put in a smaller fuse most of the time it would not be able to handle the current coming, through making it blow. wiring like the other guys said is a big issue to. but you could always use OHMS law and some other formulas to help figure out what gauge wire and fuse you need.
hope this helps
jeremy