Depends on where you want the icons edited. You can edit the toolbar icons by right-clicking the toolbar, then clicking “Edit Button”, selecting the buttons you want to change, then changing the icons.
I would recommend that you make a macro instead, which would allow you to still use the previous buttons, but would also give you the option to use new buttons with new names and with new text commands, but they do the same thing as the old button.
To do that, type “Macros” into the command bar, then add new. In the command for each, paste these in each respectively:
For Waterline Plane: '_CPlane _World _Top
For Station Plane: '_CPlane _World _Front
For Button Plane: '_CPlane _World _Right
And call the macros whatever you want. You can then hook these up to buttons by right clicking a toolbar and adding a button.