How to find a contextual menu on in icon when the right click on that icon doesn't show an option for properties. I'm trying to change an icon on Mail

[larrydonline]

bird because their default is very faint on my taskbar. I can hardly tell it is there unless a number lights up to indicate a new email. Previous help site said I need to find properties on the icon and there will be a place to change the icon. Any hints or advice appreciated.