From the image you have sent I can see a leaf turning up at the tip and turning brown. The most common cause for this tip burn is too much fertilizer especially if the plant food was not watered in or if  you used a liquid plant food on a dry plant. Leaf burn can also be caused by transplanting a hydrangea then letting the soil dry out or growing a plant in a small pot and letting the soil in the container grow dry. I would suggest you just remove the most damaged leaves and keep the soil moist. Hydrangeas do not like hot afternoon sun so move the plant to a spot where it only gets morning sun and do not fertilize. If you do transplant your hydrangea to a larger pot or into the ground make sure you break up the root ball and add some organic matter to the planting hole to help the roots stay moist. The good news is your plant should recover as hydrangeas are tough shrubs and can survive some mistakes in their care. Keep growing, Marianne Binetti