Did you replace the calipers? If not, you don't have to bleed the system but it's good maintenance to get the old fluid out since it will have absorbed moisture. Open the bleeder screws, crack the cap on the master cylinder to prevent a vacuum from building, and let the fluid run out. Keep the reservoir filled with clean fresh fluid. When the fluid coming out is relatively clear at one caliper, close the bleeder screw and move on to the other one.
If you did replace the calipers, did the master cylinder run empty? That makes bleeding more involved. To avoid that, place a stick between the seat and brake pedal to hold the pedal down about an inch while the hoses are disconnected. That will stop the reservoir from running empty. When you do start bleeding, you might have to irritate the brake pedal a little to get the fluid to start flowing. Close the bleeder screws when no more bubbles are coming out. Stroke the pedal a couple of times to wash any remaining air bubbles into the calipers, then crack the bleeder screws open once more for a few seconds.
Some people think you have to have a helper to push the brake pedal to pedal-bleed the system but gravity bleeding is just as effective. One thing of major importance whenever pushing the pedal is to never ever push it all the way to the floor. Crud and corrosion build up in the lower halves of the master cylinder bores where the pistons don't normally travel. Pushing the pedal all the way down runs the lip seals over that crud and can rip them. At first that will result in a slowly sinking pedal when you hold steady pressure on it. Eventually you'll have no brakes.
Also be sure to avoid getting any hint of grease or other petroleum product in the brake fluid. That is a very expensive mistake because the only proper repair is to replace every part that has rubber parts that contact the brake fluid, and to flush and dry the steel lines. Most professionals even wash their hands before working on the hydraulics to prevent getting fingerprint oil in the brake fluid.