I've done this one year when my income was excluded, so I could convert up to the standard deduction + personal exemption tax free. It was pretty easy. I used Vanguard. Here's a link to do it:
https://personal.vanguard.com/us/ConvertToRothI think I had to convert to a money market fund, then moved it into the fund I wanted. It worked easily for me.
If you're still working, you might not need to start converting immediately, unless your freelancing won't pay for all the bills. If your freelancing is making lots of money, then you should continue contributing to a 401k and IRA, and don't start the conversion until when you retire.