Removal of text values in data

Hi, I'm scratching my head - I'm dealing with data collected on paper and entered manually where the vast majority is numeric, lots of binary variables - but occasionally someone has written 'not sure' which has been entered into excel. I've imported this into stata 13 so now I can't change the variable type from string.

Does anyone know a function that will search for cells containing non-numeric values and replace these with a missing value?

all thoughts much appreciated.
You have two options:
Excel: Highlight the column and click Find and Replace, type "not sure" and replace it with " "
When you import it to Stata, treat it as missing value (.)

Option two, use Stata:
replace var1 = substr(var1, "not sure", " ",.)
destring var1, replace