The official FAQ doesn't say a great deal about editing one's own questions. The most relevant part that I can see is under What if I don’t get a good answer? where it states:
First, make sure you’ve asked a good question. To get better answers, you may need to put additional effort into your question. Edit your question to provide status and progress updates. Document your own continued efforts to answer your question. This will naturally bump your question and get more people interested in it.
Neither the How to Ask page nor the Community FAQ add any further insight into what are appropriate edits to one's own questions.
The Edit questions and answers privilege states (emphasis added):
Some common reasons to edit are:
- to fix grammatical or spelling mistakes
- to clarify the meaning of a post without changing it
- to correct minor mistakes or add addendums / updates as the post ages
- to add related resources or hyperlinks
Whilst the above relates specifically to editing others' posts, I would urge you never to change the meaning of any post (including your own): it can be confusing for others who thought they had already considered your contribution (and perhaps commented or cast a vote).
Besides which, it's counterproductive for you:
you would then have a (hopefully) good question with a lot of down-votes, which makes your question less appealing to people browsing question lists (and therefore less likely to be answered); and
there may also be close-votes (which require 3000 rep to see), which put your good question at risk of being closed prematurely.
If the original question can be salvaged, attempt to do so with appropriate edits: it could help others who experience a similar issue in the future.
If it's unsalvageable, the appropriate action would be to flag it for closure (or cast a close vote once you gain that privilege) rather than delete.