Tips to improve

[Tempest-Blue]

So I just started learning how to surf and I'm having trouble transitioning to bigger waves. I'm also having trouble being able to duck dive. I learned on a 6'10 x 19 x 2 shortboard and it's really difficult for me to duck dive whenever I try to push down the board it doesn't really go down and I'm 5'9 160 lbs. As for the bigger waves I can stand up and ride smaller waves just fine but I can't really go across diagonally so when I try it on big waves I just end up wiping out or pearling and launching forward. Sometimes I end up at the top of the wave where it crests and I fall down and the impact throws me off balance and I wipeout. Whenever I watch the experienced locals even if they are at the top of the wave they seem to be able to ride down the wave unlike me where I get some air on my board and hit the water then wipeout and their board seems to always stay horizontal and on the water. Any tips on tackling those bigger waves and carving the face or at least being able to ride the face and is it even possible for me to duckdive my board because whenever I see those other surfers their boards are shorter and super thin.