I will explain step by step how to make a PSP theme.

1. First you need the PSP theme creator software, it is called custom theme converter. You can download it for free.
2. Then adobe photoshop software to edit the image.
3. Open the custom theme converter. In the information tab, enter some title, product ID and version for your PSP theme.
4. Make the wallpaper. Open the wallpaper with adobe photoshop and resize it to 480×272 pixels and save it in format (.bmp) with 24 bit color. Then import in the wallpaper tab.
5. Then in the category icons, make the icon with 64×48 pixel image size format and then click file, save for web, PNG-8 thing and 256 color format (important, or your icons will break in PSP Themes Creator).
6. In the first level icons tab, you need to create the icon with 48×48 pixel image size format and then click file, save for web, PNG-8 thing and 256 color format.
7. Then in the second level icon tab, just create two icons, the default icon and the settings icon. Make the icons with 32×32 pixel image size format and then click file, save for web, PNG-8 thing and 256 color format.
8. Next in the others tab. Make a preview icon with 16×16 pixel image size format and then click file, save for web, PNG-8 thing and 256 color format. Also create a preview image with 300×170 pixels and save it in 24-bit color (.bmp) format.
9. And finally, click on the file, then export and save as .ptf file format.
10. Your PSP theme is ready to put on your PSP.

Thanks for your attention.