Yes, you can drive the old ones out with a mallet or a punch, some sort of BFH to provide adequate encouragement for them. You'll see that you can rotate the hub and that there are certain places where there is more clearance than others to remove or replace the studs from the back.
Rotate the hub so that you can insert the new stud as far as possible. Place a stack of washers on the stud and use either a flat lug nut (available at most auto stores) or a lug nut put on backwards and draw the stud in by turning the nut until it is pulled _all_ the way into the hub. A little oil on the threads usually helps.
If you use the conical part of a stock lug nut to pull the stud in you'll likely deform the bottom of the lug. If you have an extra one to sacrifice this isn't a big deal, or use a flat one.