If you plan to fly, the nearest international airport is Birmingham. From the airport, you should take a train into Birmingham New Street station before boarding a CrossCountry service out South Wigston. The festival site is then a 25 minute taxi ride away.
If you plan to travel by rail either from (or via) London, you can take an East Midland service from St. Pancras to Market Harborough. It's then a 20 minute taxi ride on to the festival site.
If travelling from north of Leicester, you can either travel into Birmingham or Leicester. The latter is a 25 minute taxi ride away.