It looks like the plant is being watered using overhead watering and the exposure to water for long periods of time may be causing these leaf spots. Those are fungal/bacterial infections. The pictures resemble symptoms of Bacterial Leaf Spot, which does start at the bottom of the foliage and moves upwards and the spots are concentrated along the leaf veins like in the pictures. Some browning on the leaf edges however can indicate the need for soil moisture but it is hard to see if the leaves reflect that type of problem. When the leaves lack water, the edges eventually turn brown and then the leaves continue browning inwards but I did not see that. I would cut off the worst of the leaves & dispose in the trash (disinfect the pruners when done), water only the soil -never the leaves- as best as you can (if using a sprinkler, water close to sunrise to reduce the time that the leaves stay wet; try soaker hoses or drip irrigation) and use clean sanitation practices: throw plant debris like dead flowers and dried out leaves/stems in the trash; keep plants so they do not touch each other's leaves, which allows for more air movement and more rapid drying of foliage; applications of some copper-based fungicides in late spring can be used to help limit disease spread (note: these fungicide applications are not likely to be very effective in warm conditions). Sometimes, you may need to destroy the plant if the disease gets out of control. If so, do not plant another hydrangea in that same spot.