Simple you cannot. The Bermuda is not dead, it is dormant, alive, and well. If you did not bother to keep up your Bermuda, what makes you think SA will do better with neglect?

I know it's not dead, I'm not an idiot. And I didn't say that I'm going to neglect the st augustine. I neglected the bermuda because I don't like that type of grass because it's very invasive.

thanks for your awesome input.

I had a good laugh reading this thread. TW may have just seemed short in his answer but he does know his stuff.

Anyway...
You will need to kill the Bermuda before you plant anything else or it will come back and take over. When the Bermuda is actively growing (depending on your location) late spring this summer start the process.
Water and fertilize to get it growing real well. Then in a week or two spray glyphosate (RoundUp, etc.). Repeat process of watering, fertilizing and glyphosate every 7-10 days thereafter, multiple times (3 to 4). You think it is dead and it is not. Bermuda is very difficult to completely kill. I will repeat, very difficult to kill.

I am not a St. Augustine grower but I think late summer/ fall you can plant it. Others that know better than I can answer this more definitively.

I live in a growing community - from several thousand to eighty thousand in 10+ years. The grass planted in the early stages of the city was St. Augustine -- probably all Floratam, which is the grass installed at my house -- mid-Florida -- when purchased. This past spring/summer I replaced most of the St. Augustine with Empire Zoysia plugs. A combination of a cold winter and fungus killed most of my St. A. a year ago. The Floratam cannot accept regular Southern weed killers that are okay with Zoysia. About 5 years ago the developer stopped with St. A. and started with Zoysia. St. A. requires more fertilizer, water, and weed killer, will not accept much foot traffic, and is far more susceptible to fungus.

Thanks for the advice guys. I did a some reading around here and it looks like Texas does know his stuff, but don't know why you had to response in that way. I'm sorry for using the incorrect word "dead" what i meant was dormant.

I might just have to stick with Bermuda after reading a lot stories about failing to completely eliminate Bermuda.
I'll just need to level the lawn since its uneven in a lot of areas and reseed the Bermuda.

You can do it but you are going to have to wait until the Bermuda is growing aggressively to nuke it with RU, or solarize it during the heat of summer. It is one thing to eradicate it with a few sprigs here and there, but completely different thing when your yard is Bermuda and try to replace it with a less aggressive grass. It can be done but you are talking a whole summer worth of work and a life long battle keeping it under control. It is kind of like the War on Drugs. You lost the war before you even declared war.

I'm not sure the real answer has been written yet. We really need to know:
Where you live (at least the city especially if you live in SoCal).
Do you have any watering restrictions?
Do you have any shade on the lawn?
Are you willing to mow 2x per week?

As TW has said, if you want to kill the bermuda, wait until summer (June depending on where you live). If you want to keep the bermuda and level the lawn, also wait until June.

If you want to mix bermuda with St Aug, that can be done, too. You do not have to have a monoculture. One minor problem with that is that they each thrive under different conditions. If you mow high and water once a month in the cool weather and once a week in the heat, the St Augustine will tend to overrun, but not eliminate, the bermuda. If you mow low and don't water, then the bermuda will overrun the St Augustine. If you have any shade, the bermuda will die out and St Augustine will move in.

Sapphire and Floratam are two very aggressive st augustine and can compete with bermuda as long as you water deeply when needed.

And plant enough trees so that bermuda can't thrive with less sun but enough for st augustine to thrive.