There's no easy way...
Hit PAGEs.. Scroll over to files then the sub catagory Waypoints. This should be a list of all your waypoints. You'll have to select and edit each one. When you scroll over each icon in the list you should be able to select and it will pull up a box with 50 different options to pick from. Select the one you want ( stump, blue fish, red fish, X, etc.. Then hit save. Repeat the process.
It's a little easier with a TOUCH unit because you can touch the field you want to change such as name, icon, etc.. But it's a tedious process, which will make you keep them better organized and make the changes when your making each waypoint.
Hope this helps!