Before you start upgrading your EP account to a newer version it's strongly recommended to backup both EP SQL database and EP installation folder. Backups allow you to rollback to a previous EP installation in case of the upgrade will fail.
If the upgrade failed you need to do the following:
1) Open the 'MS SQL Server Management Studio' and restore Easy Projects database from a backup to a new name, or to existing one (in such case please make sure that the 'Overwrite the existing database' box is checked).
2) Delete all files from your EP installation folder.
3) Make sure that your Easy Projects site or virtual application in IIS points to the EP installation folder, e.g. 'c:\Inetpub\wwwroot\EasyProjects\'.
4) Make sure / set up a dedicated Easy Projects application pool in IIS to use the right version of ASP.NET (ASP.NET v2.0 for EP v7 and older, ASP.NET v4.0 for EP v8 and later).
Note that EP v7 and older uses the "Classic" managed pipeline mode of an application pool.
5) Once the above actions are completed try to open your Easy Projects website.
In you still experience any problems please contact EP support at firstname.lastname@example.org