From Ground: First, water the red-seed dandelion plant to dampen the soil. This makes it easier to remove the plant without damage. Dig a generous circle around the plant with a shovel, taking care not to cut into the root ball. Lever the plant gently out of the ground with the shovel, lifting from underneath.
From Pot: Water the potted red-seed dandelion generously, and then turn the pot sideways. While gently tugging on the base of the stems, tap the edge of the pot to loosen the plant. If it doesn't slide out, you can carefully run a knife around the inside edge of the pot.
From Seedling Tray: Use a dibber or a pencil to ease the seedling out of its cell. Be careful not to pull on the stem; instead, lift from the roots. If the seedling is small, you can turn the tray upside down and gently tap until the seedlings fall out.