How do I export my Thunderbird emails to my new gmail apps account?

Howdy! So, I had a bunch of emails on a free gmail account. I wanted to get a paid gmail, and so they had to purge the old email. Long story but I migrated all of my contacts, sent emails, and inbox emails to Thunderbird. So I have since set up my new gmail. ANd I managed to export the contacts back from Thunderbird to my new gmail, but now I want to export my emails that I have stored on Thunderbird to my new gmail. How can I do this? Cheers...