Today I had upgrade a CA from Standalone to Enterprise. Here is a chacklist:

Backup

1. Backup the CA using the CA Management Console. Right-click on the server name in the console and under All Tasks select Back up CA.
2. Select the following options:

   

3. Enter a password for the export files.
4. Click Finish to start the export.
5. Test restoring the database on a lab computer with the same name.

Reinstall

1. Uninstall the Certificate Services from Add/Remove Programs, Add/Remove Windows Components.
2. Uncheck the checkbox to uninstall.
3. Go back to Add/Remove Windows Components and check the checkbox for certificate Services.
4. Select Enterprise Root CA and remeber to check “Use custom settings to generate the key pair and CA certificate”
5. Click import to import the backed up root cert, click Yes to overwrite the old keys
6. On the screen for Certificate Databaser Settings click “Preserve existing certificate database”
7. Done

Links

http://technet.microsoft.com/en-us/library/cc785411.aspx
http://support.microsoft.com/kb/298138