Peel (if you want to) the peaches and remove the pits. Cut into 1/2"-1" chunks and place in the pot.
Squeeze the juice from 1/2 of a lemon over the peaches and stir.
Sprinkle the sugar over the top of the peaches. Do not stir.
Close and lock the lid, turning the steam release valve to closed. Press Steam and adjust time down to 2 minutes (or manual setting.) If Steam setting only goes down to 3 minutes, then watch closely and simply turn off after 2 minutes of cook time has elapsed.
When the cooking cycle has ended, allow a natural pressure release for 5 minutes. Then turn the steam release valve to open to release any remaining pressure.
Using a potato masher or something similar, break down any large chunks of fruit. Mashing it up helps to thicken the jam as well. Depending on how juicy the peaches were, you may have liquid to cook off or thicken.
Simmer on Brown/Saute for 5-7 minutes to cook off some of the liquid and thicken. It will thicken and gel more after cooling. If you want to, you may also use a corn starch slurry (1 tbsp cold water mixed with 1 tbsp corn starch) to simmer with it and thicken that way.
Remove from pot and add to jars to cool and thicken. Makes 1 pint of jam.