To those who are facing a similar issue, below is the solution:
Dim sdeWs As IWorkspaceFactory = New SdeWorkspaceFactory()
Dim workspace As IWorkspace = sdeWs.OpenFromFile(sde_path, 0)
Dim x As DataManagementTools.UpgradeGDB = New DataManagementTools.UpgradeGDB(workspace, "NO_PREREQUISITE_CHECK", "UPGRADE")