Harvest:
Pick raspberries when the fruits are ripe. Ripe fruit will be soft and come away from the plant with little effort. Unlike blackberries, the plug or core remains behind on the plant when you pick the fruit. Unripe raspberries will not ripen off the plant.

For more information on growing Raspberries, check-out this great guide from Harvest To Table:
https://harvesttotable.com/how-to-plant-grow-prune-and-harvest-raspberries/