If you install Windows 7 and don’t enter an installation key, the 30-day activation clock starts. To see how many days you have left, click Start, right-click Computer, and choose Properties. At the bottom of the dialog under Windows Activation, you’ll see the number of days left in your trial period.
When that number gets close to zero, you can extend the free period another 30 days via the following steps:
- Step 1 : Click Start-->All Programs-->Accessories. Right-click Command Prompt and choose Run As Administrator. 
 
- Step 2 : Type the following command and press Enter
 
slmgr  -rearm
-  Step 3 : Restart Windows 7.
 
Once the OS restarts, the Properties dialog described above will indicate that Windows 7′s activation grace period has been reset to a full 30 days.
You can run the -rearm trick a total of three times. If you perform a -rearm at the end of each 30-day period, you end up with 120 days of full, unfettered Windows 7 use without having to supply an activation key. 
  
 
 
 
 
              
          
          
        
          
        
Here are the steps to convert trial version IDM to full version : 
- Download and Run KeyPatch from here...
 
- Click "Clear Previous registration data".  
 
- Choose "Patch Server Check" -> Search File "IDMan.exe" in Installation directory. Usually directory at C:\Program Files\Internet Download Manager
 
- Click on "Generate". This is your Serial Key.
 
- Then, Run IDM.
 
- Click on Registration and choose registration...(don't select order online)
 
 
- Fill Form : 
    First Name : Up to You
    Last Name  : Up to You    
    Email       : Up to You
    Serial     : Copy Serial from KEY PATCH IDM.exe 
 
- Finished...Enjoy full version IDM.
 
- Do it Same if happen Fake Serial Number because you update your idm.
 
- I have used and tested it on my IDM v 6.05. It works!
 
- Please, Share your views in comments.