switching from sqlite to postgres in rails app I´m working on

I am rather new to rails and I was thinking about how much trouble is it to switch from sqlite to postgres in an app that I´m currently working on. The thing is I have never switched in a middle of the building App process.

My local database has some data, but it is not relevant and may be deleted. I´m more concerned about the tables, columns, models, etc...

My reasons for the switch are:

1. I want to be able to use the 'groupdate' gem with my 'chartkick' gem in developement.

2. Later I will deploy to Heroku, I have done that before with adding 'pg' gem to production.

I have Postgres installed on my computer and I also have Postgres.app. I´ve been testing chartkick with groupdate in another project, so Postgres is not the problem.

So the question is basically, how much trouble is to switch from sqlite to PG in a middle of a project and what is the easiest and fastest way to do it?

sorry for the long text, hope someone reads it :)