If you want to change the "desktop wallpaper" you can go to Tools -> Settings -> Phone -> Standby Mode -> Background Image -> Click on "Yes" and then select the image you want to put as background.
If you want to put an image instead of the operator name (in the right corner, between the clock and the battery meter) you need a more complicated "trick":
- download and install eFileManager or SeleQ
- now go and create some folders in the phone under C:\system\Apps ... create the folder Phone, and under this one create the folder Oplogo
you should have this folder created:
- now you can put inside this folder (with eFileManger or SeleQ) the pictures you want to use as "operator logos"
- Click on image you want in Oplogo folder and scroll down to
- Click on SET AS OPERATOR LOGO
- Phone will reboot and new logo will be up
- Job done
- size of these pics must be 97x25 pixel
Mine are .jpg.
I USE SELEQ.