Enable auto-update
In Subscription settings, each subscription has an "auto-update interval (minutes)" — set a value (e.g. 1440 for once a day). Then confirm "update on startup" is enabled in Parameter settings, and v2rayN pulls fresh nodes on schedule.
Via proxy or direct
If the subscription domain is abroad and direct updates fail, set it to "update via proxy" — but you need at least one working node, or you hit a "no node → can't update → still no node" deadlock. Keeping one node that doesn't depend on the subscription avoids this.
What happens after
An update replaces the old same-named group with the new list. If you hand-edited some node parameters, an update may overwrite them — keep important custom nodes in a separate group not tied to the subscription.