If you disposed of qualifying property such as small business corporation shares and qualified farm and fishing property, you could be entitled to the Lifetime Capital Gains Exemption. To claim the exemption, you will need to fill out Form T657, Calculation Of Capital Gains Exemption.
To do so, you will need to know your, proceeds of disposition (the price you sold the property for plus any fees associated with the sale), adjusted cost base (the price you paid for the property plus any improvements that you made), and any exemption you may have used in the past. If you don't know this information you can contact CRA as they will be able to provide you with this information.
For more information on the Lifetime Capital Gains Exemption, see the links below: