I did this a while back on a full size Chevy pickup.  Aren't they held into
the control arm by 3 rivets on an S-10 also?  I just ground the rivet tails
off, knocked them out and removed the old balljoint.  The new ones were held
in by high strength bolts.

Garrett Fulton

I've done it both ways - pounding 'em out with the "tuning fork"
wedge, and using a press.  Most BJ presses have accessories to also
assist in removing the old ones.  I highly recommend using the press
to get them out - if you don't have the right accessories to your
press to do that, then most auto parts suppliers will rent suitable
presses to you reasonably.  Do NOT heat up anything with a burning
torch; you may destroy the temper of the surrounding metal and weaken
it.

Obviously your going to have the vehicle supported on jack stands under the
frame rails.  Remove tire, remove the caliper and hang it out of the way
with a coat hanger, you don't have to do this, but I find it gives a little
more room, and no chance of damaging the hose. Pull cotter pin out of
castled nut and loosen it but don't take it all the way off  Support the
lower control arm on a jack as close to the ball joint as you can but don't
cover it, turn the wheel so you have access and hit the top of the castled
nut with a 5 lbs hammer a good whack.  That should "break" ball joint loose
from the spindle.  If you use the pickle fork to break it apart still leave
the castled nut on the ball joint until it pops loose.  If you have a
compressor and an air chisel they make pickle forks for them as well.  Do
not get the all in one kind where the forks are inter-changeable on the
hammer shaft, they break.
Once the ball joint is broke loose from the spindle, remove the castle nut
the rest of the way and lift the spindle off the ball joint and then tie it
out of the way, I use a good bungee cord to pull it foreword in the wheel
well.  With the jack still under the control arm you can use the ball joint
press to get the old one out, use the afore mentioned 5 lb hammer and whack
it sharply on the top of the stud a couple off good hits and it will come
out, or if you have an air chisel use a blunt punch and drive it out that
way.
Installing the new ball joint use a ball joint press, do not grease the
outside of the ball joint nor the inside of the ball joint bore in the
control arm.  Make sure you have the ball joint started straight.
As has been stated no flame wrench on the control arm.  Besides the
possibility of weakening the unit due to messing up its temper, you can end
up with an over sized hole that wont hold the ball joint properly.  Torque
the nut to spec and use new cotter pins, and then  grease it good.  If after
torqueing, the hole in the shaft doesn't line up with an opening in the
castle nut, tighten it a bit more till it does,  Do not loosen it to get
them to line up.
Whitelightning

Use a pickle fork.

Bud