How can I move money from 1 ROTH IRA to another?

Pretty much the title. I've seen for other accounts in Fidelity I can move funds relatively easily, but what would be the best way to move funds from one Roth IRA to another? I have one that I haven't invested to in a little while and want to move the funds and reinvest it into my other Roth IRA that is much more diversified. Thank you.