How to change a Tax return after filing
If you need to make a change to any return you have filed with the CRA, do not file another return for that year.
Wait until you receive your notice of assessment before requesting any change to a return. You can only request a change to a return for a tax year ending in any of the 10 previous calendar years. For example, a request made in 2013 must relate to the 2003 or a later tax year to be considered.
To adjust a return, visit the CRA page http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/chngrtrn-eng.html to view the options available
You can make changes to the return Online, or by mailing in a T1-ADJ form and any supporting documents required.