Yes, you can delete a preset by going to the Preset Library, right-clicking a Preset, and selecting “Delete From Library”.
There is no way to edit a preset and have all instances of that preset be updated across all of your Programs. If you add your “echo” preset to another Program and then overwrite the preset, this will create a new Preset with the same name and add it to the library.
If you start with your “echo” preset, edit the Parameters, and save the Program instead of the Preset, you will now have a Program with different “echo” Preset parameters without saving another copy of the “echo” preset. Note that changing these “echo” Preset parameters will not affect other Programs with the same Preset.
Alternatively, you can give unique names to your presets such as “1/4 note echo” or “echo 200ms” to avoid confusion.