From Design Dashboard > Theme settings > Logo Header.
You should watch this tutorial video to know details.
1.1. Logo SVG
You can go to Shopify Dashboard > Files > Upload the image, then Copy the name image & paste it to Logo SVG box.
2.2. Logo (Require)
You can upload logo image from your device.
If you have already use logo SVG, you can’t use Logo (require) anymore. These options only allow you to use one of them.
2.3. Logo Retina (Option)
Retina option uses for Apple devices. Because the pixel density is higher than the standard threshold, the Retina display will provide a smoother visual experience with softer curved corners. When you upload logo image Retina, all customers’ devices which are Apple will be see logo Retina.
Both logos can be changed width by dragging a horizontal bar.
2. Logo sticky
This option only actives when you enable Sticky header on Header settings. Go here to find more.
It allows you to stick logo when you scroll down. You can choose logo image or another feature image.
It is the same with the settings for Logo, you can also change the width and add the Retina for Sticky logo.
3. Logo Mobile
It is the same with the settings for Logo, you can also change the width and add the Retina for Mobile logo.
4. Logo transparent
This option only actives when you enable Header transparent on Header settings, and only show on Home Page. Go here to find how to Enable Header Transparent.
So what is Header transparent? Header transparent is a tool to help the header on the background of the content instead of having to spend a space dedicated to the header.
Without Header transparent:
It is the same with the settings for Logo, you can also change the width and add the Retina for Transparent logo.