You can easily download custom icons from the web. Put them all in a folder where ever you like. I have mine in Pictures.
1. Unpin any of the icons on your taskbar that you do not like.
2. On desktop create a new shortcut for each of the apps you had pinned, right click it, select properties, select change icon, point it to your folder where you saved the new icons, pick an icon, Apply OK.
2. Right click on the new desktop shortcut, select pin to taskbar
4. You can then delete from the desktop if you want.