You could try something like:

select top 5 left(Full_Name_Field, CHARINDEX (' ',Full_Name_Field, 1)) as First_Name,

right(rtrim(Full_Name_Field), len(Full_Name_Field) - CHARINDEX (' ',Full_Name_Field, 1)) as Last_Name,

from customer_Table

where Full_Name_Field like '% [a-z]%'

update customer_Table

set

First_Name...