Are you able to set up a 24 volt system in your 12 volt land rover to run a 24volt winch?

Yes, you will need to install a second 12V battery in series with your existing 12V battery to supply 24V to the winch. However, to keep them charged, they have to be charged in parallel. You'll need a schematic to do this correctly and not damage the winch or batteries. I recommend you contact the winch manufacturer for a schematic. It might be best to purchase two new 12V batteries to operate the winch and not tie into your Land Rovers battery. I would purchase "deep cycle" marine batteries such as are used in boats and RVs. These will give you the best performance They are available anywhere batteries are sold.