Because you can be re-assessed for up to 7 years after the initial assessment, it is a good idea to update your tax file to reflect the changes and print or save an updated pdf copy (for TT Online). This way, what you have for your records will match what the CRA has on file. (Be sure that you have a pdf copy, as your return will disappear from TT Online after next year.)
As it turns out, unless the discrepancy is the result of an error in data entry, you can't really update TT Online tax files to conform to the assessment, particularly if the difference stems from a discrepancy between the CRA's calculation and an amount calculated by TurboTax. The CRA's numbers do prevail (unless you contest them) in any case, so just keep in mind that your notice of assessment overrules your saved PDF copy for any future reference.