How do I record Troop Leadership positions?
Internet Advancement does not track leadership positions. If you want to track them, you should use Scoutbook.
How do I convert to that?
The advancement database for IA2.0 and Scoutbook is the same, so there isn’t any conversion, per se. You should not use IA2.0 and Scoutbook at the same time, however, since they operate slightly differently, and can produce apparently conflicting results (e.g. marking items as Awarded is an automatic step in IA2, but requires intentional action in Scoutbook, so that leaders can actively track whether or not a particular award has been presented to the Scout).
Using Scoutbook involves logging in at www.scoutbook.com with your my.scouting username and password. The interface is reasonably self-explanatory, IMHO, but I’ve been using Scoutbook now for several years (since before the BSA purchased it).
There are a number of good getting started guides here, as well as a variety of other how-to and FAQ documents at the same site.