Ask HN: How to convert free users to paid users?

I built a side project (a chrome extension targeting a specific group) and in the first week have about 140 users signed up. Awesome right?

The problem is, that all of the users signed up for the free plan of my service (I have a free tier with limitations and a paid plans without limitations)

I've gotten great feedback from users on the app itself, and all the metrics I record from the app indicate that people are using it, but I guess I am struggling how to convince them to pay for the upgraded version.

Have any if you encountered this issue and overcome? Are there any strategies that HN users could recommend? I've tried offering coupons, email users directly (the Hi I'm blah, founder of blah... Type emails) but with limited success.