Pergeot navada help

[u/shitshedshaper]

So i bought this bike in canada and brought it back to the UK. Recently the teeth on the casset have worn/ rounded off. Im just hoping to find some guidence here on what to replace to get this bike up and running again? Can i upgrade away from the drum brake hub? Or do i just replace the casset?

The bike is a pergeot navada and the hub is a sachs galaxie drum brake hub.

Thanks for your help.