stuck on replanting orchid plants

Assuming it's a regular moth orchid (phalaenopsis), the main thing is it doesn't go in soil. Use orchid bark mix and a pot only just big enough for the roots, ideally one with lots of holes. Best time is after it finishes flowering. Ease it out, shake off the old media, and cut away any roots that are brown and mushy or papery and hollow. Firm green or silvery ones stay. Leave the aerial roots that are growing out of the pot alone, they're normal. Water lightly after and keep it out of direct sun for a week or so while it settles.