At the moment each of the pages of your website probably includes a rather dull grey box containing the word 'logo'. This is where your logo is supposed to go.
The first thing to do is to get your logo into your computer in a suitable format. Carrelet will accept files in the following formats:
Most scanner software can produce files in at least one of these formats.
Once you have the right sort of file, go to the Carrelet control panel, find the row that says Upload image file called ... for all pages ('logo') and click on the button labelled something like browse in the middle of that row. Your browser should open a window showing files on your hard disc. Move around until you find your logo file, select it, then click 'open'. In the control panel, click on OK at the end of the appropriate row.
If all goes well, there should be a pause while your logo is uploaded, and then you should get a message to say that the logo has been updated. Reload one of the pages of your website to see what it looks like.
You can change the logo at any time by repeating this process.