Are you sure you want to "remove" 9.3.1? Or do you want to *upgrade* to ArcGIS 10.0?
Either way, the details are in the documentation (just use the upper left search field with
"Uninstall ArcSDE" or "Upgrade ArcSDE" or "Install ArcSDE"). Please do make sure you're
using a supported SQL-Server 2005 build (SP2 or SP3) before you start the upgrade process.
- V