first you need to use something like polygrip(denture glue. start out using a small amount bite down hard for a few seconds,if that not enough you have to start all over again...add some more if you need it. try eating moist foods first...........chewing slow ..maybe in front of a mirror also try freedent gum.......you might have to eat small bits...using your front teeth....................good luck
With a set of Complete Upper and Complete lower denture, you must eat with both sides and chew only on the back teeth. If you try to bite at the front, it may cause instability. The above mentioned, given that your denture has a correct bite.