You have no idea how simple it is! All you will need is photoshop, your fantasy and a little time.
Open the file in Photoshop
In the list of layers, select the layer that you are going to edit.
With "type tool" replace the text with yours (make sure to download and install the fonts first)
Now do the same with icon and tag line layers. You may replace, change or delete it.
Now open the layers tab and select "merge layers" and then "merge visible"
Here u go!
Try before buy? Download here free logo template and give it a try.