1) play the minor triad, the middle note is the relative major. E.g Am= A C E and the middle note C is the relative major.
2) count up a minor third interval. I.e a tone and then a semitone from the note and you get your relative major. E.g A, a tone above A is B and a semitone above b is C and there you have your relative major which will be C.
easy as pie :)
