Optio S40;How do I delete a picture set as "welcome screen"?

I set one of my pictures as start-up screen, but I changed my mind and I tried to completely delete it from the memory. That wouldn't happen. I formatted my SD card, the built-in memory, i reset the camera, but nothing helped and every time I go to "setup", "screen setting","start-up screen", this photo is still available along with the default "optio" screen.
How can I delete it? Thanks!

It's a bit odd but it can be done

press Menu then move to the set-up menu and down to screen settings

In there you should see start-up screen use the right hand arrow to navigate into then next screen

On this screen at the bottom there should be 3 option
DISP Image
MENU Exit
OK OK

Press on the DISP button on the back of the camera
Your current startup screen should appear choose either the left or right arrow button and the Optio screen should appear
click on the OK button and system return to camera mode

if you switch off now you should see the optio screen and not the picture

hope you undestand the navigation and it works