In general, it's easier to remove food from silicone trays. Any shape of silicone tray works for JELL-O. When JELL-O sticks to the trays or molds containing them, it can rip. After JELL-O rips, you can't repair it. It will then lose its shape. Only remove the JELL-O when it's completely cooled and formed. Removing the JELL-O before it's done causes a liquidly mess.
Put a sink topper in a sink to close the drain.
Fill the sink with two inches of hot water.
Hold the bottom of the silicone tray containing the Jell-O in the water for 20 seconds. Do not completely submerge the tray.
Turn the silicone tray upside down over a plate. The JELL-O will slide out onto the plate.