Unable to import demo and install plugins

Hello seller,
I have purchased HIGHEND theme but its not working correctly, also unable to import demo. some of the messages are as follows:
Unpacking the package…
Installing the theme…
The package could not be installed. The theme is missing the style.css stylesheet.
Theme install failed.

Unpacking the package…
The package could not be installed. PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature

The installation and activation process is starting. This process may take a while on some hosts, so please be patient.
Installing and Activating Plugin Essential Grid (1/2)
Downloading install package.
Unpacking the package…
Installing the plugin…
Plugin install failed.
Plugin activation failed.
Installing and Activating Plugin Revolution Slider (2/2)
Downloading install package.
Unpacking the package…
Installing the plugin…
Plugin install failed.
Plugin activation failed.
can you help. Thanks