I've no idea how to accomplish this within the confines of an Informix database (you do realize this is a PowerBuilder and related products Q&A forum, right?)
Using PowerBuilder, one possibility would be to use a filter expression in a DataWindow/DataStore. If you use a filter expression that contains the "Match" DataWindow expression function, such as:
Match(columnname,'[^0-9]')
Any row where that column contains only digits will be filtered (removed from view), leaving only the row(s) that have one or more non-numeric characters.
You can easily write a PowerScript function that examines each character of a string value and discards any character that is not a digit. Note: What will you do if the string contains NO digits?
Then simply loop through all of the non-filtered rows (i.e., all of the rows in the DW/DS's primary buffer), use your "clean up" function to assign a sanitized value to the column in each row, then dw.update().
Of course, you need to be smart about this... If you have a large number of rows to be examined, you'll probably want to retrieve them in reasonable-sized chunks (for example, 10,000-25,000 rows at a time). I suggest you retrieve only the primary key columns and the column(s) to be cleaned instead of the entire row, particularly if the table contains a lot of columns.
Once the data has been cleaned, you might wish to consider adding some input validation to prevent dirty data from being entered by the users in the future.
I hope this gives you some ideas. Good luck!
John