As long as the current instance was deployed starting from 5.1.x and newer, you should be fine.
As far as I know:
1. stop all cell services
2. upgrade the bits using the .bin file
3. run the db upgrade script (if required)
4. Upgrade the host agents
- this can take a while since it'll put the hosts into maintenance mode ... so only upgrade as many as you can handle at one time (per cluster).