Hi,
This is an easy problem to sort out. You need to use the substr function which has the format substr(fieldname, character to start at, number of characters to take). So to take the left 6 characters of a field your start position would be character 1 and you would need to take 6 characters.
To give you an example put this line of code in a data step (you will need to change the field names to fit your dataset):
newfield=substr(oldfield,1,6).
Hopr this helps!