From the compatibility chart, this is the upgrade path for NPM:
Network Performance Monitor (NPM)
Upgrade Path
Orion NPM 7.8.5 ⇒ 8.5.1 ⇒ 9.1 ⇒ 9.5.1 ⇒ 10.1.3 ⇒ 10.3 ⇒ 10.7
So if you ar on a version between 9.1 and 9.5.1 then the first install would be the 9.5.1 then 10.1.3 etc
You may have to request the older versions are added to your Solarwinds portal.
As you are upgrading from a pre 10.0 version it would also be a good idea to check the resource requirements which are on page 41 of the NPM admin guide
http://www.solarwinds.com/documentation/Orion/docs/OrionNPMAdministratorGuide.pdf
You have some very nice features to look forward to