To see them, click on the Map Mode button (lower left) on the screen and turn on Custom Waypoints.
To delete/edit them: long-press on one of them (not just normal momentary press or click), then choose Edit Custom Waypoint. That presents you with a dialog box. You can quickly delete that waypoint with the Delete button, or you can change the name by clicking on the name up in the upper left.
To see/edit/delete all your custom waypoints, do the same steps to bring up the dialog box for one of your waypoints, and click on the box in the upper right that says Group. The group name that contains that particular waypoint (and I assume the other) will be in that box (probably "Default"). Anyway, click on the Group box, then choose Edit Current Group. That will bring up a list of all the waypoints in that group. As you click on each one it will shift the map to show you where it is. You can then choose to Edit it, which brings up the individual waypoint dialog box you saw earlier. Or you can choose Options, then Edit Multiple Waypoints. That presents you with a checkbox list where you can select any/some/all of your waypoints. Click Next, which then presents you with a dialog box with some choices (which among others, includes Delete).