Use the handle of a knife and give the lid a few good whacks along the edges around the surface of the whole lid. Use a rubber glove to give you an extra grip. This was a favourite with our grans. Be careful you donâ??t hammer it too hard, especially if it has just come out of the fridge. I have been known to break the glass this way!
Lightly moisten a dishcloth or towel and grab and twist, or run the lid under a hot water tap, for at least a minute. Tip it up so the water reaches the seal underneath.
Rubber bands can do the trick as well. Have two broad ones in a kitchen drawer. Wrap one just under the lid for a better grip and the other on the lip of the lid. Grab with both hands and screw in opposite directions. If the jar has already been opened, maybe it is not the seal that is stuck but some of the contents which has spilt over the edges.
You can also try by giving the bottom of the jar a good thump.