Steps Involved:

Step 1: Download the IDM trial or If you already have IDM installed Update it by going to Help---}} then to check for Updates.
 If you don't wanna update your version, Just click on Registration.
Step2: When you click on registration, Now a new dialog appears that is asking for Name, Last Name, Email Address and Serial Key.
Step3: Now Enter you name, last name, email address and in field of Serial Key enter any of the following Keys:

RLDGN-OV9WU-5W589-6VZH1
HUDWE-UO689-6D27B-YM28M
UK3DV-E0MNW-MLQYX-GENA1
398ND-QNAGY-CMMZU-ZPI39
GZLJY-X50S3-0S20D-NFRF9
W3J5U-8U66N-D0B9M-54SLM
EC0Q6-QN7UH-5S3JB-YZMEK
UVQW0-X54FE-QW35Q-SNZF5
FJJTJ-J0FLF-QCVBK-A287M

And click on ok to register.

Step4: Now after you click ok, it will show an error message that you have registered IDM using fake serial key and IDM will exit. Now here the hack starts.

Step5: Now Go to START --}} Then go to RUN  and type the following text and click enter:

notepad %windir%\system32\drivers\etc\hosts

For Windows 7 users, due to security reasons you will not be able to save hosts file.
The trick is below: 
First of all go to C:/ drive then go to Windows Folder and then go to System32 folder and then go to Drivers folder and then go to Etc Folder, in the Etc folder you will see the hosts file.
Now right click on hosts file and go to its properties, then go to security tab and then select your admin account, just below u will see an edit button (in front of change permissions), Now give the user full control and write and read rights and then click on apply and then click on Ok, now u will be able to edit the hosts file and save changes in it.
 

Now copy the below lines of code and add to hosts file as shown above:

127.0.0.1    tonec.com
127.0.0.1    www.tonec.com
127.0.0.1    registeridm.com
127.0.0.1    www.registeridm.com
127.0.0.1    secure.registeridm.com
127.0.0.1    internetdownloadmanager.com
127.0.0.1    www.internetdownloadmanager.com
127.0.0.1    secure.internetdownloadmanager.com
127.0.0.1    mirror.internetdownloadmanager.com
127.0.0.1    mirror2.internetdownloadmanager.com

After adding these piece of code, save the notepad file. And exit from there.
Now start your Internet download manager, and now you IDM has been converted to full version and specially when you update next time, your registration will not expire. That means it will remain full version for life time and you can update it without any problem.

I hope you all have liked my post.