If you have changed the clutch line, clutch master cylinder or clutch slave cylinder in your VW, then chances are you have introduced air into the clutch system. Air in the clutch system causes hard shifting or no ability to shift gears because the air in the fluid will compress, and the clutch won't disengage. To ensure that all the transmission components work together properly, you will need to bleed the clutch. Fortunately, bleeding the clutch is simple and is similar to bleeding your brakes.
Jack up the VW and place on jack stands.
Push down on the clutch pedal and, while pushing down, count, "1, 2, 3" and on 3 say, "holding." This will inform your helper when the clutch pedal is fully depressed.
Instruct the helper to attach a clear rubber tube to the clutch slave cylinder bleeder and use an 8mm wrench to open it when the clutch pedal is being depressed. The helper will open the bleeder at count 1 and close shortly after the clutch pedal is fully depressed.
Repeat Steps 2 and 3 until you don't see any bubbles of air going through the clear rubber hose. At that point you should feel the clutch pedal to be a little harder to press down than before.
Lower the VW to the ground and test the clutch system for proper operation. If the clutch remains "mushy" or "soft," then you may have to repeat the entire process again until all the air has exited the system.
You can purchase a one-way bleeder that you can install on the clutch slave cylinder. The one-way bleeder acts like a check valve and will only allow air out so that you can bleed the clutch by yourself without fear of getting air in the system.
Wear safety glasses when bleeding the clutch.