Not sure what version of Office you have...
In Office 2003, the help file says to do this. It worked for me.
Edit a logo for a personal information set:
Open a Microsoft Publisher-designed publication that contains a logo, or
insert a logo placeholder as a personal information component.
How?
On the Insert menu, point to Personal Information, and then click Logo.
If necessary, reformat the information, and resize and move the component.
To edit the logo, select it, and then do one of the following:
To change the text in the logo, click the text box in the logo and then type
the text you want.
To change the picture used in the logo, subselect the picture, right-click
the picture, and then choose the picture you want.
To change the logo design, click the wizard button and make the changes you
want in the Logo Designs and Logo Options task panes.
To replace the logo with a logo picture file that you already have, click
the wizard button, click Logo Options in the Logo Designs task pane, click
Inserted picture, and then click Choose picture to locate the picture file.
Hope that helped.