As with any mortgage term, at the end of your 2-year mortgage term, you can renew your mortgage with your existing lender, or switch lenders to get a more desirable mortgage product. Since you will already have had to qualify for your 2-year fixed-rate mortgage at the same standards you would have needed to qualify for a 5-year fixed-rate mortgage, provided you renew with your existing lender, you can do so without re-qualifying (as long as you’ve been making your mortgage payments regularly and are in good standing with your lender). Should you choose to switch to another lender and seek a 5-year fixed-rate mortgage with them, you will need to submit an entirely new mortgage application.
If you feel like you need to convert your mortgage from a 2-year term to a 5-year term before the initial 2-year term is done, you risk breaking your mortgage and incurring substantial penalties. Unless you absolutely need to, it’s generally not advisable to take this step. However, if you must do so, you may be able to negotiate an agreement with your current lender, depending on the terms of your original mortgage contract.