How to Install Custom Themes on PSP

1. Connect PSP to PC via USB (or insert Memory Stick PRO Duo into card reader).
2. On the memory stick, open/create folder: PSP/THEME (uppercase).
3. Copy the .ptf theme file into that folder.
4. Safely disconnect/eject.
5. On PSP: Settings → Theme Settings → Theme → select your new theme → Apply.

Only official .ptf themes work on stock firmware. Custom firmware (CFW) supports additional formats (CXMB, CTF) and dynamic backgrounds.