How to change the logo in Joomla 1.5 default template

One of the very first things we all do in a new Joomla installation is change the default Joomla logo. When you are still a Joomla beginner, this might be a bit of frustrating task, especially when you still have no idea what templates are, and how to changing template.
The logo is defined as part of the rhuk_milkyway template. It is defined in the template.css file. There are two ways to change Logo in a template.
First Way:

1. Upload a new image named logo.png using FTP software (we recommand using FileZilla) to /templates/rhuk_milkyway/images. When prompt for replace, click Yes.
Done. The site logo is changed

Second Way: (If you don't want to overwirte the default logo image)
1. Upload a new image named .png using FTP software (we recommand using FileZilla) to /templates/rhuk_milkyway/images.

2. Go to Extensions>> Template Manager click on rhuk_milkyway link and then click on Edit CSS; Edit template.css
3. Find the following CSS entry: div#logo, The full CSS entry is:

div#logo {
position: absolute;
left: 0;
top: 0;
float: left;
width: 498px;
height: 75px;
background: url(../images/mw_joomla_logo.png) 0 0 no-repeat;
margin-left: 30px;
margin-top: 25px;
}

Change the line: background: url(../images/mw_joomla_logo.png) 0 0 no-repeat;
to

background: url(../images/.png) 0 0 no-repeat; = the name of the filename of the logo you have just uploaded.

3. Change the width and height entries in the to the width and height of the new logo you uploaded.

4. Save the CSS file.

Done. The site logo is changed

http://www.wzcreativetechnology.com/joomla/joomla-tips-and-tricks/60-how-to-change-the-logo-in-joomla-15-default-template.html