The Bubble Trainer is an online application, so you don't need to download anything. You do need to use the current version of Internet Explorer, Firefox, or Safari.
You can sign up and use the Bubble Trainer for free. Full membership costs $19.99/mo.
The free plan only allows you to play 50 hands/mo. The pay plan allows you to play as many hands as you want.
Once you're signed in you can click on your account page to see your upgrade and downgrade options.