Changing the Logo throughout the site

Hello all.   I was wanting to know what page I can edit to change the logo throughtout the site.  Also what size do I need to make it so it will flow with the site?

Thanks

The image to edit is "App_Themes/darkOrgange/logo.gif" and the CSS definition for it in in "App_Themes/darkOrange/styles.css" under "a.logo".

I am a new user and I can't find this folder you are speaking of.  The only way I've ever made any changes to my NopCommerce is to use the online tools.  It sounds like you are accessing it some other way.  Can you help me get my logo changed? If there is a better way to do it like an FTP i am open to that but will need help.  

Thanks,
Richard

To edit nopCommerce you will need Visual Web Developer or Visual Studio. You can get Visual Web Developer for free form Microsoft. Do you have this?

I have Visual Web Developer but i am not at all experienced.  I had my hosting company install NopCommerce for me which they told me would be installed on the main (root directory).  I have only ever done anything on my site using the back end (administration) online.  I have no "saved" files or folders to my own computer.  I have no idea how or what i need to do.  It sounds like i need to open it with Web Developer but i don't even know if i have something to open.