Muhammad Fiki Ansyori

Before following below steps, you need to have FREE account in the respective filehosting website(whose cookie you are having and want to convert your FREE account into PREMIUM account). After signing-in as a FREE user in the particular filehosting website(Hotfile,Filesonic,Fileserve,Megaupload,etc), follow following steps:
1. Install 'Cookie Editor' firefox addon.
2. Restart firefox.
3. Now, go to Tools>>Cookie Editor.
4. Search for respective account in the Cookie Editor  search dialog box.
5. Make the following change depending on your cookie host :

You need to edit the above value and replace the content with your cookie. Close the dialog box and refresh your FREE account page. 
If the cookie is Premium and is working, then your FREE account will be converted into PREMIUM account. If it doesn't work, try with a fresh cookie and follow the above steps.
Hope, you are clear with the above procedure. 
If you are still having problem with the process, don't hesitate to ask.