How do I quit my 9-5 and work on my startup fulltime?

I've been at a Fortune 500 company for a little over a year now. Got promoted twice, and I am starting to struggle. Not because the job is necessarily difficult but because my heart is else where. I've been working on a side project that's giving signs of life. Spoken with potential customers who came to me with a problem and asked for a solution. I've tried building startups in the past and have failed because my prior projects were solutions in search of problems but this is different. For the first time I feel I have something tangible in my hands. What do I do? How do I go about this?