Click here for the Magento 2 instructions.

The easiest and fastest way to change all 3 default Magento
logos is to replace the logos on your FTP server. To do that
just login to your server using FTP and navigate to this
folder: skin/frontend/default/YOURTHEME/images. There
you find the following files:

  • logo.gif
  • logo_email.gif
  • logo_print.gif

But as you can see in the image below your theme can be build
different from the Magento default theme. Here you see the
FTP of my theme pt004. If you want to change the logo of that
theme you should go to skin/frontend/pt004/default/images/ In your own
theme it can be done differently, but the structure would be
the same

You can now replace the default logos by uploading your own
logos with the same file names. (Do not forget to flush
cache!) Done! Now you see your own company logo on all
mentioned places. OK, so far so good.

But what to do if you don’t want to use a GIF but a PNG or
JPG
? No problem! You can easily define the the logos for
each of the 3 logos in your Magento backend. Scroll down and
I will show you.

Change the default Magento GIF logo to your own PNG or JPG
logo

You need to login to your Magento Admin Panel. Than go to
System > Configuration > Design > Header. There you
can change the image name to what you want. See the image
below.

Here I explain the same as above but than in steps

Change Header Logo

  1. Upload your own logo with your to your server using FTP
    skin/frontend/default/YOURTHEME/,
    or skin/frontend/rwd/YOURTHEME/
    .
  2. In your Magento backend navigate to:
    System > Configuration > Design > Header
  3. In the Header section you find
    all settings for the logo.
  4. In the field Logo Image Src you
    can now replace images/logo.gif
    with your own filename like images/mylogo.png.
  5. You can also define the alt tag of your logo image in the
    field Logo Image Alt.

Change Email Logo

  1. In your Magento backend navigate to:
    System > Configuration > Design > Transactional
    Emails
  2. Here you find all settings for the logo in your Magento
    Emails.
  3. Here you can easily upload your Email Logo in the field
    Logo Image.
  4. You can also define the alt tag of your logo image in the
    field Logo Image Alt.

Change Print Logo

  1. In your Magento backend navigate to:
    System > Configuration > Sales
  2. In the Invoice and Packing Slip
    Design
    section you find all settings for the logo in
    your printable documents.
  3. Here you can easily upload your Email Logo in the field
    Logo for PDF Print-outs (200×50)
    and Logo for HTML Print View.

This video shows you how to change the logo without FTP
knowledge

Basic knowledge about the default logos

At first you have to know that there is not only one logo to
replace in your store. By default Magento makes use of these
3 logos: You have a fresh installation and wonder how to
change the logo in the header section? You already tried to
find a setting in your admin to upload your own logo but
couldn’t find it? OK! We have good news for you 🙂 You are no
fool! Unfortunately changing the header logo in Magento just
isn’t very comfortable. But it’s not impossible! Here you
find all infos for replacing the default logo with your own
company logo.