Google is your friend. There are tons of videos on shock maintenance. Watch several to make sure you get a better feel for what you need to do. The Granite BLS comes with emulsion type shocks. Add that to your search to get more specific info.
But the basic procedure is this:
1) Remove shock from vehicle
2) Remove spring cup and spring from shock
3) Remove cap from shock and empty old oil
4) Fill 3/4 with new oil and pump/twist the shock shaft to remove any air trapped underneath the piston.
5) Let the shock sit upright for 10-15 minutes or until air bubbles are all out
6) Top off the oil
7) Replace the cap slowly and try to get as much air as possible out of the shock
8) Put spring back on and replace shock on vehicle.
The weight and amount of oil you use and how far in you push the shock shaft when replacing the cap can affect the tuning and rebound of the shock. The springs also can be changed for stiffer or softer weights if desired. I would recommend you start with 35wt oil but you may need to go up or down from there depending on how you drive.
Also read the other threads that have other options for replacing the shocks altogether. The stock Arrma shocks have some issues if you are driving hard or jumping a lot.