Improve my riding experience I'm new to cycling and I've got a borrowed, older, road bike. I believe it's a 10 speed, with 700 series tires. From what I've been told it was a very expensive bike in the 90's. I'm training for my first century ride in Tehachapi CA and I'm riding for a fundraiser. https://www.generosity.com/community-fundraising/riding4rett and need all the help I can get.

Anyway in my training, I've discovered that I do about a 75-80rpm cadence, but I can't seem to get over 16 mph, on flat land, plus hills kill me. Does anyone have any suggestions how I can get more speed and make the hills easier to climb? I've been told I need to change my cassette, but don't know what my cassette is. Is it the rear gears? Any help will be appreciated.
No magic solutions am afraid. Train. Try an get cadence to 90 as the norm. If you want to get better at hills do more of them. Make sure you take it easy at bottom and aim to be able to have enough left to ride away at top strongly.
Also consider using heart rate zones to train