If you are upgrading with the same control panel on the same server, then Yes, you can upgrade at any time by submitting a trouble ticket with the request.
It is free to upgrade and the only charge would be the price difference in the plan you upgrade to. For example, if you were paying $1.00 per month with your previous plan with tooniehosting.ca, and the new plan is $2 per month, you'd only pay the $1.00 per month difference.
If you are wanting to upgrade, feel free to submit a trouble ticket requesting the upgrade and we will see if the hosting plans are compatible.