To change the "Everything' icon, please see:
http://support.voidtools.com/everything ... g_the_icon
"Everything" is using the incorrect icon for the taskbar (largest icon possible, rendered as small icon (16x16)).
"Everything" is using the incorrect icon for the alt-tab menu (largest icon rendered as normal icon (32x32)).
The tray icon should be using the correct icon.
Try removing the very large icon sizes from your ico file,
keeping only the small icon (16x16) and normal size icon (32x32).
The problem has been fixed for the next release of "Everything".