Sage CRM now uses by default a partially responsive contemporary theme called 'ergonomic'.

See:

C:\Program Files (x86)\Sage\CRM\CRM\WWWRoot\Themes

ergonomic.css

You should be able to change the following image

Assuming CRM is installed in the default location

C:\Program Files (x86)\Sage\CRM\CRM\WWWRoot\Themes\Img\Ergonomic\Icons\logo.jpg

Thanks, however there is one problem with this approach.

"One common method of customising the Sage CRM logo is to replace ewaretopleft.jpg with a custom image in \CRM\CRM71\WWWRoot\Themes\Img\Color\Logo. However, after installing a new Sage CRM patch, this change may be reverted."

Correct me if I am wrong here.

You are not wrong, simply create a copy of your amended logo and rename it to something like logo_keep.jpg and replace again after an upgrade.

Be mindful that a future release may change the logo dimensions, background colour etc. so you may have to redesign the default image for it to appear correct.