‘Used to’ can be used to express states and also actions.
‘Would’ is generally used to express actions.
He used to be cheerful.
He used to be proud.

You can’t use ‘would’ in these sentences to express the same meaning. You can say ‘He used to sit there for hours’. In this sentence you can replace ‘used to’ by ‘would’. ‘He would sit there for hours.’ But when there is no sense of habit or recurrence, you do not use ‘would’. Where there is discontinuance of an action, ‘used’ is used and not ‘would’.
He used to live in Calcutta.
He used to be a great speaker.
There used to be a temple here.
I used to live nearby.
My health is not what it used to be.

Also ‘used to’ expresses the contrast between the past and the present. ‘Would’ refers only to habitual past action.”