Will changing my diet improve my chances of getting pregnant after having tried to conceive for more than a year?

Diet and conception. Unless you have been on a highly restrictive diet or an unbalanced diet, changing diet may not be of help in improving the chances of conception. Multiple other factors would be much more important.
Unlikely. Unless you have an unusual or deficient diet now, changes will probably be quite small overall. A healthy diet, limiting caffeine and alcohol, avoid tobacco, moderate exercise, and staying healthy promote natural fertility. Herbs, otc drugs, diets, vitamins, supplements, and tricks - natural or otherwise - to 'make you fertile' don't work and can be dangerous.