Extrusion to a vertice

[rcrichfl]

I started my plane project from a cube, and extruded and shaped as required. Now, I have to end it up in a cone, but I cannot find the way of doing it. Following the basic Tutorials, I cut the cube and mirrored and now when I want to apply any of the ways I know to end in a vertice, the best I got was one vertice for each side of the mirror.
Did I made a mistake by starting with a Cube? Is there any way to converge from the last face to a vertice?
Attached is the file with the design so that anyone with more experience can help me, it has the original.
Thanks a lot.
  Integrated fuse 1.wings (Size: 195.7 KB / Downloads: 2)

[micheus]

You need to Frezze the Mirror before you try to change one of the sides.

[rcrichfl]

Thank you. It did work.

[rcrichfl]

Micheus, your suggestion worked as expected. Is there a way to "unfreeze" the mirror later so that when I extrude the areas towards the tail I can still use the symmetry properties of the mirror?