You want to change the dyno types that your application is using.
You can select the types of dynos that your application uses from the Heroku Dashboard.
Click on the app name, and go to the Resources tab to see what type of dyno's your application is presently using. Click Change... to open a selection of dyno types you change to. You can find more information on here.
Alternatively, you can perform the operation from the command line. Read more...