You will be able to get an approximate idea of where the shed is in relation to the boundary by taking a look at your local council's GIS database which should be viewable online.
So far as any onsite activity to locate the boundary and the shed's proximity to it that will require the services of a registered surveyor. Contact one in your area to get an indication of the expected cost of a 'boundary redefinition'. Various factors will have an influence on the cost of getting this done including the age of the original survey of your property, the title status on your property and accessability and visibility to the area in question.
So far as any onsite activity to locate the boundary and the shed's proximity to it that will require the services of a registered surveyor. Contact one in your area to get an indication of the expected cost of a 'boundary redefinition'. Various factors will have an influence on the cost of getting this done including the age of the original survey of your property, the title status on your property and accessability and visibility to the area in question.