Your PSP must be charged to at least 78% . Connecting to a power source during the update is highly recommended to prevent a "power-off brick".
To move from an old M33 build to modern CFW, you must first return the system to a clean official state. psp 352 m33 upgrade to 660
Upgrading a PlayStation Portable (PSP) Go to product viewer dialog for this item. Your PSP must be charged to at least 78%
Use a reliable, formatted Pro Duo stick or a high-quality microSD adapter . psp 352 m33 upgrade to 660