Initially release any clips by squeezing with a pliers and pushing back along the line. Lines can be prised off using a snipe nose pliers or flat blade screw driver, pushing on the edge of the line. Don't pull the lines which can stretch them.Two fuel lines leave the tank of a two stroke engine. The primer bulb sucks gas from the tank via the line with the filter on the end, gas returns to the tank via the other line without the filter. When you replace a line, to check whether they haven't been mixed up, fill the tank but leave the line without the filter above the level of the gas. When you push the primer bulb, gas should eventually squirt out the line without the filter. If the lines are mixed up, air bubbles will flow out of the filter and no gas out the other line.
For a pictorial guide and more info on troubleshooting 2-stroke engines and carburetors, see my guide here:
String Trimmer Won Work 2 Stroke Engine and Carburetor Troubleshooting