Delete from Registry using SQL

xp_regdeletevalue and xp_regdeletekey are the two undocumented stored procedures that helps in deleting values and keys from registry. These stored procedures should be used very vary carefully as there are chances of harming the system and system may crash. 

xp_regdeletekey
This is an extended stored procedure that will delete an entire key from the registry.
EXEC xp_regdeletekey @rootkey,@key
Example:-
EXEC master..xp_regdeletekey @rootkey='HKEY_LOCAL_MACHINE',
@key='SOFTWARE\Test'
xp_regdeletevalue
This is an extended stored procedure that will delete a particular value for a key in the registry.
EXEC xp_regdeletevalue @rootkey,@key,@value_name
Example:-
EXEC master..xp_regdeletevalue @rootkey='HKEY_LOCAL_MACHINE', @key='SOFTWARE\Test', @value_name='TestValue'