Yealink SIP-T54S Administrator's Manual page 214

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
Select the desired wallpaper from the pull-down list of Wallpaper with DSSkey unfold.
3.
Click Confirm to accept the change.
4.
To change the wallpaper for expansion modules via web user interface:
Click on Settings->Preference.
1.
Select the desired wallpaper from the pull-down list of Wallpaper for expansion
2.
modules.
Click Confirm to accept the change.
3.
To change the wallpaper via phone user interface (take SIP-T48G IP phones for example):
Tap ->Basic->Display->Wallpaper/Dsskey Wallpaper.
1.
Tap or
2.
Tap the Save soft key to accept the change.
3.
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, or press or to select the desired wallpaper image.