rpatel did you try using 'Find' and 'Replace'?
Here's how you can do it:
First, Very Important - MAKE A BACKUP COPY OF YOUR TABLE!
Check properties of the column, For Example, so that it allows nulls, set property to "Allow Zero Length".
Now select whole column in which you want data replaced by single-clicking header of column
Once whole column is highlighted, press Crtl + F
Click on 'Replace' tab
Enter value you want to replace in 'Find' field and new value want in column in 'Replace'. Leave 'Replace' field blank if you want to record to be blank.
After you have entered everything correctly, click on 'Replace' button.
I hope this is what you wanted and my suggestion helps.
mrkshpntf.