Handguards
1) make sure the gun's unloaded
2) find a pair of Channel Lock pliers, with the blue plastic/rubber lining around the handles
3) stand the gun up on the buttstock, then put the pliers handles around the handguard slip ring to use for leverage
4) apply downward pressure on the slip ring with one hand, and work the handguards out of the slip ring and the front handguard retainer with your other hand.
5) rest for a second
6) apply downward pressure again, this time take one of the A1 handguards and put it in, then the other.
It's a bit easier with another person helping.
Pistol Grip
1) flip the gun upside down
2) using a flat bladed screwdriver (unless there's a hex/allen bolt in there), unscrew the screw inside the pistol grip
3) slowly remove the pistol grip, being careful not to lose the selector detent/spring
4) if the spring's still in the lower, replace the A1 grip onto the lower, being careful not to squish the spring down at an angle
5) replace the screw and tighten
6) check selector functioning
Again, if this stuff doesn't work, check the tutorials and you might post pics of your setup and ask questions in the Build It Yourself forum.