Well, removing gravel is a serious affair.
If you remove all of it, you completely wipe out you nitrifying bacteria, which poses a potential threat to your fish.
If you do remove the gravel and change, it would be smart to put the new gravel in a separate tank and add 5.0ppm of CLEAR ammonia. let this go through the nitrogen cycle. This will make the trans for your fish safer.
Another thing that would be smart to do:
Buy an advanced, deluxe or whatever type power filter for your tank. these type filters have an aerobic pad that bacteria can attatch to. This will save you any losses, and you won't have to pre-cycle the new gravel BUT you need to buy ammonia, NO2, and NO3 test kits. If ammonia gets to 1.0ppm do a normal water water change. If no2 (nitrite) gets to 0.5ppm, do a water change. After the ammonia and nitrite disappear then watch Nitrates (NO3) for the rest of the tank's life. try to keep those below 40ppm
*note: allow aerobic pad to become grungy and full of bacteria before doing gravel change*
sorry if i gave you info. you already know, just wanted to cover everything.
Nets are good for removing gravel, you do need to remove the fish, and rinse all new gravel well, before adding to keep down gravel dust.