So, plenty of options for you. Going from a 36 t to a 40 t in the back might work. Depends on the rear der. Check out something called a goat link. A small pice that goes from the der hole on the frame to allow the rear der. to hang lower from the bike. Just be sure to check cassette tooth count for spacing. Some of the jumps are large. Even easier. Just get and after market 40 T cog. It will involve taking out the 16 or 17t to fit it in. On your original cassette. Wolftooth has your answers. The 40 or 42 is added. The 15 and 17 are replaced by a 16.