How can I remove the slot from the template?

I want to remove one slot from the template because I usually do not write anything under this slot.
But 68 rem already used this template, so those rem has this slot.
Since I don’t want to have this slot in the newly creating rem from now on, I want to omit a slot from the template.
But if I delete it from the template, the web browser always stops working for a few minutes, and I couldn’t remove it.
Could you teach me how to delete it?

Thanks! It was much easier than I thought.