Amend boundary on Title Plan

I wish to change a boundary of the fence line between my address
33B Fairwood Road, Penleigh, Dillon Marsh Westbury Wilts BA13 4EA
& my neighbour at 33A Fairwood Road
We have agreed I will erect a new fence between the properties
adding 900mm to the front to 4m past the rear of the house line
& from this point to the bottom of the garden an extra 460mm

Also to define the bottom position between our land & the Railway

Andrew - Please refer to the guidance on our website - https://www.gov.uk/your-property-boundaries

You may also find information set out in Supplements to our Practice Guide 40 useful - https://www.gov.uk/government/collections/land-registration-practice-guides#guides-40-to-49