The template I am using contains a logo in the header, but I do not want to use the default Joomla logo. Accessing the images folder by FTP, I found the logo and it was called: mw_joomla_logo.png so to replace it I would need to call my file the same thing and overwrite it, otherwise I would have to change the link name in the html which might take some time to find. Looking at this file I also got valuable information such as:
Size - 289 x 75 pixels
File Type - PNG
Transparency - Yes
I used this to create my own logo in Photoshop. I made it slightly bigger (300 x 77 pixels) but any larger and the logo seemed to get cut off so I made it as big as I could get away with. Here is the result:
