In BQE CORE, the company Email ID and logo in the header of invoices are brought forward from the Company screen. So, you can set and change both there (Settings > Company > Information). Check CORE Help Center for details.
The company logo displays only on invoice templates. Adding a company logo to reports can only be done via a custom report prepared by our Report Customization Team for a nominal fee.
CORE supports a 1:1 aspect ratio logo of 125 x 125 pixels and a maximum file size of 2 MB. You can use .bmp, .png, and .jpg file formats for logos. If the aspect ratio of your logo image is different from what CORE requires, the logo image will be skewed to the 1:1 ratio and appear distorted. Check CORE Help Center for details.
If you want to get it customized by BQE Software in case of non-square logos, you can email customreports@bqe.com for a quote and let them know which invoice templates you plan to use.
Also note that the sample invoices don't show your company logo. These samples can be found in Settings > Billing & Invoices > Invoice Templates and they show the BQE logo by default. When you create an actual invoice using the templates, your company logo is used, provided you have added that in your Company screen.