Try using the below code:
SELECT RIGHT(MyColumn, LEN(MyColumn) - 4) AS MyTrimmedColumn
In the above code, RIGHT takes 2 arguments - the string (or column) to operate on, and the number of characters to return (starting at the "right" side of the string).
LEN syntax is used to return the length of the column data, and we have subtracted four so that our RIGHT function leaves the leftmost 4 characters "behind".
Hope this helps you.
Note: If you want to UPDATE the table rather than just return doctored results, then you can do as follows:
SET MyColumn = RIGHT(MyColumn, LEN(MyColumn) - 4)
The above solution will keep the 4 characters at the start of the string, rather than discarding said 4 characters.