If I undstand your question correctly you want to change the background picture.

On desktop right click;
Settings --> Desktop Settings --> on Backgroud Tag click File icon --> "Select backdrop image or file" window --> on Backdrop Tag
select the image you prefer.

Or browsing File to make selection from your image correction directory

Then click [Open].  That is all

HTH

satimis

I'm using xfce 4.4 and I don't understand how to change the background (i mean choosing it) when i use a list.

I'm using xfce for years, so I will not change just for this !

Your sincerely,

Polytan