Measuring Point - remove characteristic

Ladies and Gents,

I have created a measuring point and have assigned a characteristic to it. I have then saved it and went back to change mode. I cannot seem to change the characteristic anymore as the field is grayed out. I have checked the config and all the menus and cannot see a way of re-enabling that field.

Could someone please provide some guidance on how I could change / remove the characteristic on a measuring point?

Thanks

Mantas