are you deleting the old logo and inserting the new one?
Stop being so hard on yourself!
Also, are you using the same font as the old logo to create the new logo?
Sometimes its easier to create a new image completely, in a new file, and then copy and just replace the old image with the new one.
i guess im not fully understanding the problem.
If this doesnt help, and i'm completely off target here, you could give me more information on what exactly you are looking to do and i can try again :)