Ask HN: How to change fields in tech?

I describe myself as a full-stack engineer because that is what I have the most professional experience doing, but I really enjoy growth hacking. The only problem is I have very little professional experience doing it and I'm not sure what the best way to change that would be.

I'd be interested in hearing from people here who have successfully changed fields and how you did it.

Should I start a blog and focus on writing about growth hacking?

Is there are course I should look into taking?

Should I offer my time for free in return for experience?

I'm currently looking for work so I don't have any opportunity to switch positions, although perhaps I should be looking for places which may be open to that?