It is easily!

Firstly, after purchasing, your downloadable files and serial key will be sent to your email. The file that you can download normally is a zip file, let extract it and use FTP client (like Filezilla, WinSCP, cuteFtp...) to upload (copy) all folders and files in this extracted package to your Magento site root folder. Don't worry, this task will not overwrite any existing files, it only add new files to the folder structure.

After uploading is done, let log in your Magento administration panel to refresh cache by way go to System > Cache Management. Select all caches and take action “Refresh” then submit. Besides it, let open System > Permissions > Roles and refresh your admin role (open your admin role and click save) or add all rules of extension to your admin role to system load all features of extension.

Navigate to System Configuration, if you can see tab CRM4Ecommerce Extensions or you see menu item corresponding with extension that you have just uploaded on menu bar, it means extension installed successfully. Remember to put your serial key to the Serial Key Information in CRM4Ecommerce Extensions > Settings of Module so that the module could be activated.

Now if you get Access denied error when click on the extension tab (or when you clich on menu item Settings of Module), you need to log out admin panel and log in again.

Go to Settings of Module in administration panel again and try to process, surely that everything will be made you happily.

With Magento VtigerCRM Bidirectional Synchronization extension:

After install Vtiger plugin on your VtigerCRM system, let upload file crm4ecommerce.php onto your vtiger root folder (you can find this file when you extract package

Then, let open http://{{your-vtiger-link}}/crm4ecommerce.php. If you see module information, that mean you installed module in vtiger site successfully.

Wish you lucky and success!