Milwaukee,
You have to open the image up in Photoshop / Fireworks / GIMP (or, some other image software) and you can then edit the text on the image. When you're done modifying the text, simply go to File -> Export -> For Web and follow the prompt (this process is slightly different depending on which image editing software you're using, but it's still similar enough).
When you are done, you will have a folder with all of the images that were "sliced" apart when you exported for the web; inside the folder, you will find your newly created logo... Now, you can simply upload it into your webserver > Templates > City Portal > Images folder and it will take effect. However, note that if you are using either the Blue or Orange themes, then you will have to upload your new logo into it's respective directory (ie. webserver > Templates > City Portal > Images > Blue (or) Orange).
There ya go, now you have a new, custom logo! If you need any more insight or for me to clarify things, simply send me a message and we'll work it out.
P.S.
Thanks for the review, but for now on, please either create a new thread or send a message to the author when asking questions that are not relevant to the original post... It makes it easier for us to manage responses (and, I almost missed your post, because it was tagged along on this thread).
Peace and Blessings!