Yellowing leaves on precious potted fig - help?

Thisiseclaire

I’m not much of a green thumb but am looking after a friend’s houseplants at the moment. Her beloved potted fig has started to turn yellow… I water gently once a week, so wonder if I am overwatering and should leave it, but the top leaves do droop after a couple of days of non-watering. I’ve pulled it from the pot to check the soil, and also wondered if maybe it wants to be moved to a bigger pot. But this is my friend’s very favourite plant so I want to do it right. Any advice would be so appreciated.