How to Upgrade from 3.80 M33-5 to 5.00 M33-6 PSP - YouTube
Here's my PSPs, top i bought back in 2008 modded and still on 5.00m33-6 but it's missing the kratos battery cover the other my brother got it for me for xmas this
PSP: Custom Firmware M33 source released for popular tool's 10 year anniversary - Wololo.net