[c-nsp] Upgrade to XR-IOS 3.8.1

[Jason Alex]

Dear All,
             Kindly i want to upgrade one of my routers to Cisco IOS XR
3.8.1 (Cisco 12410)
my current IOS is 3.6.1

any advice how can i make this upgrade gracefully without any downtime ?
and what are the steps to migrate to version 3.8.1


Thanks & Regards
Jason