Updating Vector depends largely on your installation method. Each installation guide provides it's own "Updating" section:
ManualUpdating from archivesUpdating from source
Depending on your topology, you'll want update your Vector instances in a specific order. You should always start downstream and work your way upstream. This allows for incremental updating across your topology, ensuring downstream Vector instances do not receive data in formats that are unrecognized. Vector always makes a best effort to successfully process data, but there is no guarantee of this if a Vector instance is handling a data format defined by a future unknown Vector version.
Because you'll be taking Vector instances offline for a short period of time, upstream data will accumulate and buffer. To avoid overloading your instances, you'll want to make sure you have enough capacity to handle the surplus of data. We recommend provisioning at least 20% of head room, on all resources, to account for spikes and updating.