How can I morph or change the polygon size of an object?

Hi, ive tried to attach an example of the help I need. I basically have a soldiers hat but i'd like to edit it to look slightly different.

I have A, B and C questions if this makes sense.

A. I would like to be able to fill in an area where polygons are missing so it smooths of the top of the helmet.

B. The hat and strap are a grouped object. I can select the strap as a surface. Id like to be able to take the strap and scale it to a slightly different size as well as morph the top of it.

C. The helmet needs to have the front section altered. I would like to be able to grab the front polygons and move them or morph them into a diffent shape justy on the front. The lower section of the example is roughy what im trying to achieve.

Can anyone help me on this please? Thank you.

Jase