If your web host has instructed you to change nameservers then you will need to follow the instructions they gave you. There can be many reasons for why your web host has decided to do this. Changing nameservers is not something a web host takes lightly.
Possible reasons for nameserver change:
-Your web host is streamlining their technical operations
-Your web host has recently or is planning to move to a different datacenter
-Your web host has changed a major infrastructure in their network operations (new IP transit carrier, new datacenter, or new IPs being used)
-Your web host was secretly sold and the new owners don’t like how the old setup works
The only way to figure out why your web host is making your change nameservers is to ask them.