The ways to replace jig saw blades will vary according to the make of jig saw.
Step 1 - Remove Old Blade
Unplug the jig saw or remove the battery so there’s no danger of it turning on as you work. On saws which use a clamp for the blade, open the clamp with your thumb as you hold the saw. With the blade facing down toward the work table, shake the unit. The blade should just drop out. If it doesn’t, pull on it gently.
Some units use a screw to secure the blade in place. It will be on the top, over the handle. Loosen this-don’t remove it-and gently pull the jig saw blade free of the unit.
Step 2 - Inserting New Blade
With a clamp unit, hold the clamp open and insert the blade, making sure you have it positioned correctly. Slowly work it home until it will go no further. Release the clamp and then try to pull the blade free. It should not move. If it move, pull it out and try again until it’s properly seated.
With a screw closure, insert the blade all the way, being certain it’s in the right position. Tighten the screw and try to pull the blade free. It should not move.