That's a wise decision. There are a lot of advantages to using aptitude. You should be ok to switch but it's said that it's not a good idea to go back and forth between the two. So you can do it now. Start out with
sudo aptitude update
just to make sure all is in order. Running aptitude without any arguments will get you the ncurses interface if you prefer that. Personally, I find it confusing and just stick to the cli.