installing a logo

probably in header.php;

find:

<div id="top">
		<div id="blogname">

change for example to:

<div id="top"> <div class="logo" style="float:left;"><img src="http://full_image_url" height="200"  width="200" style="display:block;height:200px;width:200px;border:1px solid red;"/></div>
		<div id="blogname">

in css:

in style.css, find:

#top {
    height: 185px;
    width: 1000px;
    margin: 0 auto;
	background:#000000;
}

change for example to:

#top {
    height: 185px;
    width: 1000px;
    margin: 0 auto;
	background:#000000 url(images/logo.png) left top no-repeat;
}

the #blogname style just after that might need a little left margin to allow more space for the logo.

upload the logo.png image to the images folder of your theme.

http://www.w3schools.com/css/css_background.asp

where in my theme dashboard to i upload the logo image

as the css is suggested, the image needs to be uploaded to the /images folder of your theme – this will require FTP or the file management system of your hoster – http://codex.wordpress.org/FTP_Clients

you can use the media -> add new uploader in the dashboard – and then note the full image url – and add that into the css;

fictional example:

background:#000000 url(http://www.gaentmag.com/wp-content/uploads/2012/05/logo.png) left top no-repeat;