cruiser chainring

I have been urged by my physio to give up the mountain bike and only ride a cruiser. I would like to do some rides that are longer. I find the gears too slow for longer rides on the cruiser and wonder if I should change the teeth on the front chainring. the teeth numbers are presently 32/42 Any suggestions on the best approach to make for a better ride? I live on the prairies, No hills in sight so don’t need a wide variation.