Discus are definitely beautiful and from what I've heard are more difficult to keep than a lot of other fish. If you're confident you'll be able to handle any issues that may arise then there are a few ways to soften your water and lower pH.
Depending on the current parameters of your water some things will work better than others. If you're looking for the absolute easiest and fastest way then you should look into getting an RO system. This however will also be the most expensive seeing as you'll need to buy the system itself plus you'll need to have something to add the nutrients back in. The natural way works best for water that is already lower in kH but involves the use of almond leaves, driftwood, and/or peat moss. This method will still work on water with higher kH but will take longer and require more materials to see a difference. Another option is to use products that adjust the parameters directly. For this I highly recommend seachem's buffering products. They have one specifically made for discus which could be of use for you. If you want to have a lot of plants in the tank with them then I would recommend instead looking into their acid/alkaline buffers as they are formulated for such circumstances.
I myself use their acid buffer on my betta's tank. My tap water comes out at a pH of 8.2-8.4 with both gH and kH going to the top of the scale. After using it since spring I've brought my pH down to 7.6 and kH down to about 5.