Any chance you can post some pictures showing the current problems? It'll be easier to figure out what's going on then and have ideas on how to fix it.
Yellow leaves with black spot sounds like a fungal leaf spot disease of some sort. You can help prevent it by making sure to clean up leaves that fall off (rather than letting them sit under the plant) and when you water, try not to have water hit the ground and then splash back up on the leaves. And sometimes doing a preventative spraying with fungicide in the later winter before it comes out of dormancy can help. But if it's a plant that's very susceptible to those problems, often you can do everything right and it's still going to have some spots--the only real way to solve it is to replace it with something that's not prone to that problem.
The black leaves could be a few different things--it could be that the plant got frost damaged over the winter in which case just be patient and see where it puts out new leaves, then trim off any branches that are dead. Or it could be a fungal problem if the shrub was overwatered.
