For Mobilia 5.0 and later
You can enlarge the logo by first going to Online Store > Themes > Actions > Edit Code > Sections > header.liquid and looking for these two lines of code:
<div class="four columns logo header-logo alpha">
<div class="twelve nav omega">
The first number (four) corresponds with the logo's container. To allow your logo more room to expand, increase the number four to something higher. IMPORTANT: the second number (twelve) will have to change also, so that when added together, the numbers equal sixteen.
So let's change some values to look like this:
<div class="six columns logo header-logo alpha">
<div class="ten nav omega">
In that same area of header.liquid, the logo image size can be increased by changing the 'img_url' value from the 280x to a higher number such as 580x:
Finally, head into the Header Section: Online Store > Themes > Customize > Sections > Header
In this section, you can now increase the 'Logo display width'. If you enter 1000, you can be sure the logo is taking up as much room as you have created for it.
For Mobilia 4.4 and earlier
You can enlarge the logo by first going to Online Store > Themes > Actions > Edit Code > theme.liquid and looking for this line of code:
<div class="one-third column logo alpha">
Change it to this:
<div class="seven columns logo alpha">
Next, look for this line of code:
<div class="two-thirds column nav omega">
Change it to this:
<div class="nine columns nav omega">
You can change the widths of these two lines to any number value you'd like, as long as they add up to sixteen in accordance with the template's column framework. You can read more about the column framework here: http://support.outofthesandbox.com/customer/portal/articles/1033987
Next, go to Template Editor -> Configs -> settings.html and look for this line of code:
<input type="file" id="logo" name="logo.png" data-max-width="600" data-max-height="300" />
Change the max-width and max-height values to match that of the image you're uploading for your logo (in pixels).
Finally, the last step is to upload your new logo file to Theme Settings -> Header. If you don't see any changes immediately, try changing the file name for your logo file on your computer and uploading it again.