A sys 1 doesn't have the support bar in the back all bigger systainers have. With the sys 1 you can simply use a rod to hammer the pin out from the inside.
With bigger systainers the support bar is in the way. You can use a needle nose pliers to wiggle the pin out from the top. If you're new to this, this needs some getting used to. Don't be too afraid to damage the pin, you can order them new from Festool for around a dollar.