1- Backup your database: http://msdn.microsoft.com/en-us/library/ms187510(SQL.90).aspx
2- Backup your Maps : \Program Files\Solarwinds\Orion\Maps
3- Backup your Reports : \Program Files\Solarwinds\Orion\Reports
4- If you have any modules upgrade them to the version required by Orion NPM 9.1: Release Notes
5- Keep on hand the installers of Orion NPM 8.5.1 SP3 in case you need to roll back to it (If you cannot extend the down time to solve an hypothetical issue)
6- Let the SP3 of Orion NPM 9.1 in the same folder of the installer so that it will be automactically applied at the end of the installation, before the configuration wizard.
7- Keep on hand the SQL sa account or a SQL account that has sufficient rights to modify the database structure.
8- Check on your customer portal that the License for Orion NPM v9 is available to not be stuck at the end of the installation.
9- Do the upgrade during support hours if possible in case you need assistance if an issue occurs.
10- why not some coffee, yet you probably won't have the time to drink it if the upgrade goes too fast :-)
Thanks for the detailed procedure Yann.
Do I need to uninstall the V8.5 first before installing the V9?
Actually that's more some ideas to keep in mind before you upgrade than a procedure. Do not necessarily follow the order.
No you do not need to uninstall Orion NPM v8.5 before to upgrade to v9.1 . simply run the executable on the top, it will stop the services for you and upgrade the installation.