Often, you can just pull them up from the sides with your fingers.
If you’re having trouble doing that, you can either get a commercially made key puller (we recommend the wire style, not the plastic kind) or remove the enclosure to get easier access to the edges.
A wire keypuller looks something like https://www.amazon.com/WASD-Keyboards-Wire-Keycap-Puller/dp/B00AZCGF7K