I am replacing old oven with double oven, current oven is on a 20 amp breaker, old wiring can not make out the gauge.

The new double oven is convection 27" ovens, the following is the Power Specs:

Amp Rating at 240V 30
Bake Wattage 2640
Broiler Wattage 3400
Convection Wattage 2500
KW Rating at 208V 5.1
KW Rating at 240V 6.8

What I need to know is could I use the existing wiring and change breaker or do I need to run a different gauge wire and if so which.