Depending on how dense the brambles are depends on what tool, would be the appropriate tool. Thick and dense brambles would be best cut out using power tools such as brush cutters, hedge trimmers or a chain saw.
Less dense brambles could be tackled with some Garden shears and a pair of heavy duty gloves.
if you feel like you have a severe problem it may be worth getting a professional in to offer a free quote ... something I can offer.
I wish you all the best