To install PrestShop theme please follow the steps provided below after exporting the theme :
1. Copy the 'Theme' folder from the exported folder -> Open installation folder -> Open Themes folder-> Paste Your theme here.
2. Open PrestaShop backend -> Go to Preferences -> Go to Themes -> Add new theme -> Create New Theme
'Create New Theme' button resides on lower-left corner of the 'Create a new theme' panel in the window.
3. Select Create New Theme -> fill the required fields , Theme and Directory Name should be same as the name of the exported theme.
4. Save -> Use this theme -> Finish