Hi --
You've come to the right place.
Good chunk of info on this here:
www.ptotoday.com/ptofaq.html
Specifically, some first steps I'd take:
1. Get a a copy of your bylaws (and/or your state's PTA bylaws) and review what is specifically required of you for disbanding. Armed with this info, you'll be ready to differentiate between what you actually need to do and what you'll be told you need to do (often a significant difference).
2. Continue the in-unit discussion/education process
before getting notifying state or getting state PTA involved. Read articles. Discuss the actual golas of your group. Determine what PTA services you are actually using and how you value them (or not). Get feedback from other's who've made switch. Be educated, so that the state PTA side isn't the only one you'll hear.
3. Once you're fairly confident it's the move you want to make, then start the formal process. First step in the formal process (depending on your budget, this may need to begin early): spend down your funds to at/near zero. If there are no funds to worry about/debate about, then you don't have many worries in the process. Then, notify state (if it's required), give any required notice to your membership and move forward with debate and vote.
4. You may also want to begin the process of setting up your PTO before the PTA is formally disbanded. This is perfectly OK and can help make the PTA-to-PTO transition even smoother.
Good luck. Know that tens of thousands of groups have made the switch (successfully) before you.
Tim