Difficulty engaging gears
 

I have just bought a tucson diesel 2 litre 2007 and everything worked fine. I now have considerable difficulty in selecting gears and suspect the hydraulics. Where is the slave cylinder to bleed the clutch? I have been told that it might be inside the gearbox is this correct and does the gearbox need to come out to replace the slave cylinder? Is there any other possible causes? My clutch pedal is only operational when almost on the floor.