在Wordpress中安装新主题会出现内部服务器错误错误

I purchased wordpress Ecommerce Theme from themeforest. I am trying to install this theme but after upload progress 35 - 40% it gives me internal Server error.

The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator to inform of the time the error occurred and of anything you might have done that may have caused the error.

More information about this error may be available in the server error log.