How do you tell her that you wana HAVE SEX?

Ok please if you have any sense at all you will disregard the previous two answers.

You should never rush into anything if you and your partner both feel that you may be ready to 'take it to the next level' then you should discuss it first. In my opinion you can really scare someone by 'pouncing' on them, if your partner is not ready just try and be supportive and if she is then make the whole experience as comfortable as possible.
I hope I have helped you a little.

Taking it to the next level, is all in the two of you. You may be completely ready for it the minute you blurt it out, but she might not be comfortable with it. Talk it out between the two of you and discuss a variety of topics on this. What would happen if you two have children, if something goes wrong. If one of you two accidentally catch an STD or a sexual disease. I hope the best for you two..

The way to tell her this is to get a ring and then find a time of the day when you will see each other. After you say hi and everything, you reach into your pocket and get the ring, get down on one knee and then show her the ring and say (her name), will you marry me?

If she accepts then youre on your way. If not, then both of you will have found out now and you can move on quickly, so its really a win win. Yes there is emotion either way but this is how its done.

If her parents approve you can get an informal court marriage and then plan for the wedding ceremony at a later time, although thats risky; depending on your family you arrange a wedding and wait for the ceremony to end, this next step is called the honeymoon where the newly wedded couple go somewhere private and close the bedroom door.

marriage is the best way, its what our bodies are designed for, weddings are a part of life, if you won the lottery and hired the smartest people to find out whats the best way to have sex, the answer is what I explained, you get married

Just talk to her about where she sees things going and see if you are on the same page.

You don't need to tell her, girls know that boys/men are usually distracted by sex most of the time.
I think you should be asking yourself.....what will the signs be WHEN SHE wants to have sex.

I think that you have to sit down and talk to her about it and if you don't feel good about that,don't make for do it,sex will come and go but love will not!