just check your manual.
if you haven't got it laying around, look here:
http: //nds1.nokia.com/phones/files/guides/Nokia_5800_XpressMusic_UG_en.pdf
or just scroll through your settings until you find something.
I flashed my 5800 with custom firmware, so I can't tell you how to do it. I think however that you need to go to homescreen settings as noted on page 14 of the manual.
