Cutting tool

How do i cut a circular hole in a mesh?

Remove the faces where you want the hole to be. While still in edit mode add a mesh circle. Fill in the faces between the original mesh and the circle.

GreyBeard

how about performing a boolean operation? Or would that give nasty results.

OR, select the verts of your jagged edges, after you delete them, and click on ‘to sphere’ 100% in the edit window. That is if you want a perfect circular hole. Besure the the cursor is in the middle of the circle.