Wait until your present return is assessed.
Then file a T1-adj. For the changed items. Include copies of all T5 slips being added, and receipts for the additional charitable donations you are claiming.
If you have My Account for CRA you may also use the Change My 2014 Return feature, however wait until you are assessed before you do this.
CRA will process the changes and send you a Notice of Reassessment, together with any addional rebate or request for payment.
Here's some additional information:
You already filed your tax return, it was accepted by the CRA, and
now you received additional forms or tax information or you need to
If so, you need to amend the tax return
you already filed. First, be sure the return was accepted by the CRA,
and do not change the return you already filed. Amended returns must be
filed on a new form called T1-ADJ, T1 Adjustment Request.
Follow these steps: