When you say "update" do you just mean refresh? It's very simple. Literally just a couple button pushes. Things to watch out for:
• Sounds like this is your first refresh, so not applicable here, but for subsequent refreshes you'd want to check with anyone with access to that environment that they've saved anything off that they're actively testing/working on so you don't remove their work
• Some 3rd-party bundles (or NS ones for that matter) will just work automatically after refresh. Some will require some tweaking to work. Some I think won't work period. Something to consider if you're doing testing with non-NS stuff
• If you have any integrations running, you'll have to reset the integration records and tokens after refresh
• If you have a data warehouse pointed at your Sandbox data for whatever reason, you have to be a little careful on refresh because it could potentially cause a spike in usage