The question you have is whether your rotors can be "turned" or are they so thin they need to be replaced. Each presents a different job. Let's start by assuming they can be turned.
The outer bearing will fall out once the spindle nut and bearing retainer behind it are removed. What's left is the "permanent" part (pressed into the rotor) the "race". On the opposite side, once you remove the rotor from the axle spindle is an identical set, with an added part.. a "grease seal". This you pry off and throw away. The bearing comes out and ... voila... a pressed in race. You WILL need a new grease seal, and grease is all, to repack the bearings. Take the rotor, with races in it to a shop that turns em, and they can tell you if it can be turned or not. If so, once you get it back clean the bearings and repack em and put it all back together. It is NOT a huge job. If you need a new rotor, you can either use a punch and hammer to remove the old races from the rotor, or buy new ones (although bearings come as a set so new races will come with new bearings). If you have new bearings because the rotors could not be turned, take em to the shop that turns rotors, or any auto machine shop and they will hammer or press in the races for ya, leaving you the new bearings.
How to press new grease into bearings. Some people buy the round things that hold the bearing and that let you use a grease gun. I bought one and gave it away. Here's how I learned to do it from an old Ford mechanic in a shop lebbenty sebben years ago. If I am reusing old bearings I clean the bearings first (we used to use gasoline to do this, I now use brake cleaner more often than not...) once they are clean, (or if you have new ones start here) get a dollop of grease in the heel of a CLEAN hand. with the big diameter down, press the round edge of the bearing into the grease, at the edge of the grease gob, over and over , nibbling ever more into the grease a little with each push down, until you see grease oozing out the top of the bearing. Rotate the bearing 15 degrees and do it again, over and over until you have done the entire bearing. Insert the bearing, put on the grease seal or the spindle retainer, tighter 'er up and you are done. Easy. <messy>. MAKE SURE YOUR HANDS ARE CLEAN! (B4 and after <g>). Hope this helps...
Happy Exploring
Chris