It is very simple to install it.
Please go through the following process.
1. Go to appearance >> theme >> add new theme >> upload theme zip file. Do NOT unzip and NOT try to upload folder.
2. After upload setup ZIP file that you have downloaded during purchase, please activate it. If you have lost the file then please login to postmagthemes.com with username that you have created during purchase and goto profile >> purchases. Here you can again download it.
3. Now remain configuration, there are many documents link as per your requirement. Please follow them to configure it.
But if you think it is still difficult to setup then please make a new username with admin right and send to us with link. You can delete it later. We will setup it for 15$.