Impedance Matching With L-Network, Terminology Issues
It's probably less confusing to describe an L-Network in terms of the Hi-Z and Lo-Z ports, since it only transforms in one "direction."  Referring to the sketch below, I have labeled the two ports Z1 and Z2.  The way it's drawn, Z2 must always be higher impedance than Z1.  This would be the case in your question where it appears you are trying to match a 50 ohm source to a 500 ohm load:  Z1 would be 50 ohms and Z2 would be 500 ohms.



If you need to transform your 50 ohm source to say, 10 ohms, then your source would be connected to Z2 and the 10 ohm load to Z1.  Or course, you would probably redraw the circuit so that your source is on the left, which simply means the capacitor now shunts the source instead of the load.

Just remember, with the L-Network, the capacitor always shuts the higher impedance port.