If your Mac is running but cannot support the absolute latest version (Logic Pro 11+), you can access the 10.7.2 update through your purchase history.
If you already own Logic Pro but are running an older version (like 10.6 or 10.7.1):
Here are the key improvements included in the 10.7.2 update:
Logic Pro 10.7.2: Technical Overview, System Requirements, and Acquisition Protocols
