When you click on SharinPix thumbnail it display the image in large view.

This view can happen to show a lower resolution version of the image than expected, most of the time this could be corrected/enhanced easily depending on the use case.

If you are using the high resolution screen, you may want the very high resolution version of the image to be displayed in large view. 

To do so you can use the engine icon from the Toolbar and choose HR version.

If you want to see some details, you may want to zoom in the picture.

This could be done by just double click (or double tap on a touch device).

When submitting a vectorial file to SharinPix, we render the image as a raster (webp, png or jpeg) format. 

The size and resolution of the picture is depending on parameters included in the original file.

As example, for an AI file we use the artboard size parameter from Adobe Illustrator parameters.
if you get a 500x500 pixels artboard size in your AI file it will be so rendered into a 500x500 pixels raster version in SharinPix.

To modify this, you should get into the original file and change this value. This is how to do it for AI  https://www.wikihow.com/Change-Artboard-Size-in-Adobe-Illustrator