How to Update SugarCRM 9.0x to 11.0x

Dear Helper Team,

I am using SugarCRM 9.0x Enterprise and want to update Latest 11.0x Ep How we can update please guide me for update to latest version.

We have 4 Instance 

1-Developer instance (Development coding purpose only )

2-UAT Instance ( after development code will test UAT)

3-Staging Instance (After UAT testing passed code moved to stating)

4- Main Production Instance (after stating final code testing code will move to production this is live instance)

All Instance are same replicas of  Production with single license.

I want To update my Developer instance as of now for all working functionality testing purpose if all current functionality will worked then i will update to all instance.

Question-1- if i update my development instance to 11.0x then is others instance working same version 9.0x or automatically updated.?

               2-is update all instance manually.?

              3- how we can update only my development instance 11.0x and other instance same as 9.0x as of now.?

              4-After testing how we can update all instance ?

              5-directly we can update 9.0x to 11.0.x ?
              6-We can degrade if we found any issue ?