Skirmish theme pic?

Hello.

This is my first post as i am having some trouble with the theme of my website.

Firstly i would like to use the “Skirmish” theme. I have downloaded and installed it however i would like to change the ship picture to one of my own. How do i do this? Please give me a step by step guide as i am very new to all of this.

Second there is a column down the right of the screen showing “archives” etc can i get rid of this element? If so again how do i do this please?

Thanks in advance!

Paul