First if you want to save anything important like say your Angry Birds achievements, certain data, etc... then you should download and install MyBackup Root or Titanium Backup from the Market and perform a backup.
I will assume at this point you just want to get updated to stock EC05 Froyo and then you can root or whatever you like after that is complete.
[INFO]
Go to the following thread below, use procedure #1 to upgrade your device to Froyo EC05.
[WARN]This will completely wipe your device clean and it will appear factory stock with official Froyo EC05 as if you purchased it brand new right now.[/WARN]
[How to] Factory Restore (or Fix a Bricked Phone)
Once you have completed this then you can root your device again using our guides and then re install either Titanium Backup or MyBackup Root to restore your backups.[WARN] I strongly suggest that you re download any apps that you are restoring data to first in the Market. Then with your backup application select
RESTORE DATA ONLY because you are bringing data from a completely different version of OS (Eclair) over to Froyo. This will minimize conflicts.[/WARN] [/INFO]
Any other questions that may arise please feel free to ask.