German Shepherd are known for their beautiful double coats, which shed heavily and naturally, specially during weather changes, you can't completely stop it shedding but can manage it not to shed that much with the right care, tools and techniques, here's some tips to manage and reduce it:

Regular Grooming:- 

• Bathing : Bathe your German Shepherd daily to keep their fur clean, healthy and manageable. use Dog shampoo and conditioner to maintain natural oil of their fur.
• Brushing: Try brushing your German Shepherd's coats regularly, after taking bath dry it off and then brush it to prevent matting, you can also use a de-shedding tool like a Furminator to reduce shedding.

Diet and Nutrition:-

• High Quality Food: From preventing them shedding, you should feed your dog, high quality dog food enrich with Omega-3, fatty acids, which will help in coat health and reduce shedding.
• Supplement: Also you can add supplements like, flaxseed oil or fish oil in their diet with the consultation of your veterinary. 

Environmental Control:-

• Vacuuming: Regularly vacuum your home, specially on the areas, where your pet spends most of their time or where your dog sleeps.
• Washing Dog Bedding frequently: Wash your dog's bed frequently to remove shredded hair from there and keep that place clean to  manage their health.

Seasonal Care:-
During shedding season, increase the brushing even more and try using de-shedding tools even more often. 

Conclusion:
Managing shedding in German Shepherd is normal, but you can definitely manage it by care a-little more, like regular grooming, a healthy diet and of-course with the environmental control, by following these tips, you can reduce the amount of hair it shedding and keep it's coat healthy.