My hair was blonde to start then I dyed it black and now I want to go bck blonde will it be OK to go back to blonde

That is one extreme choice you will regret if you want a full head of hair in the future.

Black to blonde is not a good idea. I would suggest letting it grow out to about one inch and having all the black cut off. Otherwise anything else in the way of removing the black at this point will destroy your scalp and forget about keeping the length, if it is considerable.

Tick

It's possible. I would know because I have done this a few times now. I have made the mistake from going dark dark brown to blonde in one step. I ended up with fried, ugly, orangish, brassy hair. You should do it gradually, not drastically. No, you do not have to chop off all your hair, BUT you should definitely give it a good trim after each color. Now, when you go to get your hair color, DO NOT go to a drugstore and pick out a color and expect it to be that color. Go to a beauty supply store such as Sally's. You can get a color that is 3-4 shades lighter than your hair now, but make sure you get a neutral color. That will help in preventing any funky, unwanted colors. Make sure you get a developer that is compatible with the hair color you choose (I would use a cream color not the liquid). Get a developer that is 30 volume. I would wait 6 weeks in between coloring. By doing that, you will reduce damage to your hair. Also, make sure you get a good conditioner. Sally's has one by Loreal called Nature's Therapy. Hope this was helpful! Good luck!

If you're going to try to change your hair color darker, try the lightest shade that closely matches what you eventually get to. Once you go too dark, remember this, Color DOS NOT remove color, Found that out the hard way. But you can always go darker.
If you are trying to go lighter and have colored your hair a darker shade , same thing Color won't remove color. Even if it's been 6 months, there is artificial pigment in the hair that hasn't been cut off.. If you've never colored your hair,( virgin hair, it's called)and want to go lighter, Stay 1 half inch away from your scalp ( the scalp is the heat zone and processes much faster), it will get pale yellow and you will not be able to achieve the results you want,and over process from the scalp and very damaged hair will eventually break off. It will take a while to lighten before you go back and do the scalp. Being 1 half inch away,in sections, small sections, Use a color brush and paint it on. All your hair should have color on it except the scalp People get scared when they see the orange brassy while lightening their hair, and rinse it out before it's time and then end up going back to darker. All hair goes through the brassy stage,as long as it's not on your scalp, you're OK, You may need help to go lighter, Going darker, you start at the scalp, if it's a retouch do only the scalp after it's finished timing, add shampoo to the rest of the color and massage through all your hair. The shampoo cut's the peroxide volume and refreshes the rest of your hair without damage, best done with a bottle. Hope this helps