Unless you want to buy idm online, the only way to register idm is to crack it so follow this tutorial by my friend
We all love idm but unfortunately, it is not free. This is exactly how i cracked mine.
First you unsinstall your copy of idm at the control panel >programs and features> idm.
select complete during installation.
download and install either utorrent (http://utorrent) or tixati(http:// tixati.com)
Go to http://kickass.to and type idm with crack in the search box.Click on download torrent.
install the idm, make sure that it is nor running ( exit idm after installation)
copy the contents of the crack folder you downloaded and then paste it at C:/windows/Program Files/Internet download manager.
restart your computer and idm should be registered now. NOTE=====NEVER UPDATE CRACKED SOFTWARE NEVER!!!!!!