How to Download Themes on Ps3
Theme Settings
Adjust settings to customize the XMB™ screen for items such as the background or the font for on-screen text.
Theme
You can adjust settings to customize the design of elements such as icons or the background that are displayed on the XMB™ screen. The theme can be adjusted using any of the following methods.
Selecting a preinstalled theme
Select a theme that is preinstalled in the PS3™ system.
Downloading a theme onto the PS3™ system
When you download a theme from 
(PlayStation®Store) or by using 
(Internet Browser), it will be automatically installed on the PS3™ system after the download has been completed.
Installing a theme using a game disc or commercially available Blu-ray Disc video software (BD-ROM)
To install and use a theme file that is contained on disc media, select the 
icon under 
(Game), and then select the theme file that you want to install. The theme will be used as the system theme automatically after the installation has been completed.
Creating or downloading a theme on a PC
When you download a theme from a Web site or create a theme using a PC, make a new folder named [PS3] - [THEME] on the storage media, and then store the theme in this folder. Theme files must be saved with the extension [.P3T].
To install the theme in the system storage of the PS3™ system, connect the storage media that contains the theme file to the system, and then select 
(Settings) > 
(Theme Settings) > [Theme] > [Install].
Hints
- An icon that is not part of the theme file will be replaced with another icon in the theme file or will remain as the default XMB™ screen icon.
- If a theme file contains multiple backgrounds, the theme background will change randomly.
- PC software is available that allows you to create your own theme files for use on the PS3™ system. (Commercially available software for creation of the graphical elements is also required.) For details, visit the SIE Web site for your region.
- A USB adaptor (not included) is required to use storage media with some models of the PS3™ system.
Deleting themes
Select the theme that you want to delete, press the 
button, and then select [Delete].
Color / Colour
Set the background color / colour of the XMB™ screen.
| Original | Set to the original background color / colour. |
|---|---|
| (color / colour swatch) | Select a color to set as the background color / colour. |
Background
Set the background used in the theme or the image selected as wallpaper under 
(Photo) as the background of the XMB™ screen.
| Brightness | Change the brightness of the background. |
|---|---|
| Original | Set to the original theme. |
| Classic | Set to the [Classic] theme. |
| (theme name) | Set to use the background for the theme that was set under [Theme]. |
| Wallpaper | Set the image that was selected as wallpaper under (Photo) for the background. |
Font
Set the font type to be used in the XMB™ screen or in messages under 
(Friends). When the system language is set to Korean, simplified Chinese characters or traditional Chinese characters, this setting cannot be selected.
Hint
The fonts that can be selected vary depending on the system language in use.
Source: https://manuals.playstation.net/document/en/ps3/current/settings/themesettings.html#:~:text=To%20install%20the%20theme%20in,Theme%5D%20%3E%20%5BInstall%5D.