To update your theme you need to follow the below-mentioned steps.

1: Download Latest File

Goto your account at StyloThemes and download latest theme files.

2: Deactivate & Delete Current theme

Deactivate your current theme from Appearance > Theme (Simply activate any other default theme). 

Now you can delete the current theme by clicking on it and hit the delete button in the popup.

3: Delete Stylo Core Plugin

Make sure to delete the StyloCore plugin. Go to Plugins > Deactivate StyloCore & Then Delete, you will see a delete link when hovering over the plugin name.

4: Upload Latest Theme & Activate

Now go to Appearance > Themes > Add New and upload the new theme file you just downloaded. Install & Activate and then Install StyloCore and any Recommended plugin by the theme.

5: Make sure to clear any cache before testing the updated theme.