I need to change my pressure tank I got a 3/4 hp jet pump what size of tank should I put thank s a lot

The larger the better. Put in the biggest one you can.

As a general concept the life of the pump is determined more by the number of times it cycles on and off than the amount of time it runs. The larger the tank the less frequently the pump cycles on and off.

What size is on it presently?

We are assuming this is a bladder tank. Correct?