Μετάφραση:Ο άντρας πρέπει να διαλέξει νέο δικηγόρο.
Right, and this is something throughout Duolingo that I don't understand: it's a distinction without a difference. In English, "to need to" and "to have to" (in this sense) are completely interchangeable. What difference between the two are you trying to convey? Is there an actual difference in Greek?
Yes, there is a difference and they are not always interchangeable. It's about the difference between necessity and obligation, but it may take a philosophical look on things to tell the difference.
For example: You need to eat in order to survive. You also need to keep warm etc. but you don't have to. You can still choose not to. Eating/keeping warm are needed in order to survive, they are requirements, but you don't have to.
"Have" has more to do with (moral/social/legal) duty, which you can choose to ignore. In the example above, you have to take care of yourself if, say, not doing so is a sin. It's the less frequently seen "you ought to".
Other examples: You have to do your homework (because it's your job as a student, you ought to) but you don't need to, the world does not depend on it and you might as well ignore the whole thing. You need however to do your homework if you want to get good grades, it's a prerequisite. But you don't have to. :)
Sometimes need and have are interchangeable in greek. For example, if you want to make a cake from cake batter, you both χρειάζεται και πρέπει να το ψήσεις (to bake it). However...
I don't know if introducing "must" would make things any clearer or worse. As you may already know, both "have to" and "must" are translated in Greek with "πρέπει". This could potentially open a whole new grey area of meanings, or hopefully "must", as it shows a) certainty about a situation or b) strong obligation, explains a bit better the shades of the greek "πρέπει". You, as a native English speaker, could tell the difference between the two "πρέπει"? Surely, you must bake the cake if you want one, but do you really have to? I guess the "You need to eat in order to survive." example could become "you have to..." or "you must..." but there will be slight changes in meaning.
Overall, I'd say stick with the necessity vs obligation for "χρειάζεται/need" vs "πρέπει/have to/must/ought to" and don't use them interchangeably in Greek. I hope this helps a bit.
Edit: I changed "and" to "or" between the two meanings of "must".