Changing ip addresses for NS records

[Bind Mailing List]

We are an internet provider and we have 3 DNS that have authority for more than 2500 domains. We would like to change the 3 ip addresses of these DNS but we want to keep their names. We know that the registrars have records of their names.
 

Do they have records of their ip addresses too (for these NS records)?

 

What do we have to do before changing theirs addresses?

 

Which steps do we have to follow to avoid any problems?

 

Do you know if the registrars can change these adresses for all of our domains (soa) automatically?

 

What could arrive with the root servers?

  

The registrars are icann.org, cira.ca ...

 

Thanks a lot for your help!