Hi,
I`ve played violin for a long time and I`ve always felt comfortable playing with a forearm vibrato, but recently my teacher told me that I should change it to a wrist vibrato. i`ve been watching a lot of the great violinists and some do vibrato with forearm. Anybody can tell me the difference???

Generally your forearm vibrato will be, let me think of a word, I guess wider. It will cover a greater amount of physical space on the fingerboard, and it will be closer to the notes above and below it. I must agree with your teacher though, wrist vibrato will be much easier when you get into 16th, 32nd, 64th etc. playing with vibrato.

Do whichever vibrato you want. In higher positions, wrist vibrato is easier. With arm vibrato, playing chords is easier.
Your best bet is to learn three of them: arm, wrist, and finger vibrato.