Well...it will.
When you write an UPDATE you have to specify exactly which records should be affected - or SQL will assume that you mean all of them, just as it does when you do a SELECT:
SELECT * FROM MyTable
Will return all records.
UPDATE MyTable SET MyColumn=6
Will change all records.
If you want to limit the rows you return, then you use a WHERE clause:
SELECT * FROM MyTable WHERE MyColumn=6
Similarly, if you want to alter only specific records, you use a WHERE clause on your UPDATE:
UPDATE MyTable SET MyColumn=6 WHERE MyOtherColumn=1
I have no idea what column of your table is significant here, so I leave it up to you to decide which column determines the update criteria!