is that the only fish in your tank? a gravel swap shouldnt take too long, tho im not too familiar with that specific gravel so i could be wrong.
what i would do is (in order):
-wash the new gravel very well. any way you prefer.
-drain about 30% of the tank
-transfer the fish into another container (20g tubs work great) if you want with a heater, but the fish wont die from a few degrees change (might wana boost your house temp if you are not using the heater)
-use a shop vac (clean if you have one, i keep a 10g one just for this) to vac out all the old gravel
- (optional) clean the tank, and or do a full w/c
-lay the new gravel
-carefully (with out stirring up the new stuff too much) fill the tank back up.
dechlorinate/treat the water the way you see fit. attempt to get the tank water within 1-2*f of the fish's water
add decor, and fish. enjoy.
i did this in my 55g swapping out silica sand for a mix of all sorts of planted gravels, worked fine for me. i had to clean all the diatoms off the side of the tank, thats why i added in the cleaning step.
hope this helps