Start by peeling and pitting the peaches, and then chopping them into small chunks about 1/4 to 1/2 inch in size.
If canning, prepare a water bath canner, jars, lids and rings before you start cooking the jam.
Place the chopped fruit and lemon juice in a deep-sized jam pot. Be
sure that it doesn't come up past halfway full before you start
cooking, as the jam will foam up, and you need that extra space.
Turn the heat on the stove to medium-high and cook the peaches for a few minutes so they start to release their juices, mashing the peaches for a smoother jam or leaving them whole for a chunky jam.
Stir in the pectin (but don't add the sugar yet).
Ensure the pectin is fully dissolved, and boil the jam for 1 minute.
After a 1 minute boil, add the sugar, and stir to dissolve.
Return the mixture to a full rolling boil and boil 1 minute.
Remove the peach jam from the heat and ladle into prepared jars.
For a freezer jam, use straight sided freezer jars and leave 1 inch headspace. If canning, use canning jars and lids, and leave 1/4 inch headspace.
If canning, process the jars in a water bath canner for 10 minutes (or 15 minutes if above 6,000 feet in elevation). Once the processing time is complete, turn off the heat and allow the jars to sit for another 5 minutes before removing them to cool completely on a towel on the counter.
After 12-24 hours, check seals and store any unsealed jars in the refrigerator for use within the next few weeks.
Properly canned and sealed jars of peach jam will maintain peak quality on the pantry shelf for 12-18 months, but be safe to eat so long as they're sealed. Refrigerate after opening.