ACS 5.x has a migration guide, it's actually fairly simple. Take a look at:
http://www.cisco.com/c/en/us/td/docs/net_mgmt/cisco_secure_access_control_system/5-8/migration/guide/migration_guide.html
First read the document so you understand the process and the system requirements. The utility can only be run on a 32-bit windows server running the same version of ACS 4.x as the database backup. Keep in mind it only supports specific versions of ACS 4.
Note: I've managed to perform this on the same server of ACS 4 without having to make a seperate migration machine, worked fine. This may not be officially supported by Cisco though.
What it boils down to is:
1) Downloading the migration utility either directly from the ACS 5.x web gui or using the Cisco Secure Access Control System-Installation and Recovery DVD.
2) Copying it to the migration machine and extracting it
3) Running the utility and migrating what objects you wish. Keep in mind you'll need connectivity to the new ACS 5.x machine.
4) That's it.
