I can understand Hungarian pretty well but i cant speak it.
What is the best way to learn how to speak Hungarian?
As Judit has mentioned: the only way to learn how to speak a language is actually speaking it. So either you find a Hungarian skype or conversation partner, or you move or travel to a Hungarian-speaking area, of which there are few to be found outside Hungary.
To tell the truth, I would offer my services as a skype partner, but these days I am quite busy, I barely find an hour off. Language exchange sites can help you a lot, though. Oh, and one more thing: it may help you a lot to write first, before you start to speak. Thus you practice to form your own sentences in Hungarian, to put your thoughts into words, so it may ease speaking later on.
Just out of curiosity, where are you from? What's your native language?
There is only one way - find someone who speaks and practice with them. As I assume you are in Europe you have a huge advantage over me - you can Skype within a reasonable time zone.
Also consider one of the immersion Summer Schools - for instance Debrecen has a great one 2 or 4 weeks (http://www.nyariegyetem.hu/kurzus.php?id=8) and there are scholarships available which will pay tuition and accommodation if you are selected.