Its quite easy, as long as you have a steady hand and in a room with very good light.
Just last week I refoamed a pair of LE14A woofers, did it on the kitchen island counter, directly below a skylight.
After cutting off the old surrounds and gasket, if there is one, its just a matter of applying glue to the cone's edge (usually the back) and fitting the new surround to the cone and pressing the two together with your fingers.
Then you let it dry for 24 hours.
Then the next day you apply glue to the frame, lifting up the edge of the surround, as you work your way around, and press it into place. If there is a gasket, or ring, then you glue it on top of the edge of the surround and frame.
Again, let it dry for 24 hours.