FHA loan refinance to conventional

[Chandler Smith]

I read an article awhile back about refinancing an FHA loan to a conventional loan. If I remember correctly in order to refinance you must have 20% equity in the house. So my question is: If I bought a house on an FHA loan/203k and did a rehab, then got a new house appraisal showing a 20% or more increase could I then refinance to a conventional loan? If I did get it refinanced to a conventional loan would I be eligible to rent or sell the house? Does this violate any FHA regulations? Sorry newbie here