If you're using your Marriott Bonvoy points, it's just matter of paying more points for a higher-category room (or suite).

If you're using a Free Night Award (FNA), it won't work for a "Redemption with Points Upgrade." FNAs can only be applied to simple Redemptions. Let'e suppose you have an 85K FNA. At the hotel you want, a Redemption for a standard room is 50K points and a "Redemption with Points Upgrade" for a junior suite with a good view is 80K points. You can only book the standard room with the 85K FNA, even though the FNA value exceeds what you would need for the upgraded choice.

Marriott.com makes it easy to apply an FNA for a Redemption, but impossible to apply an FNA to a "Redemption with Points Upgrade." That's not a bug. It's consistent with the Marriott Bonvoy Loyalty Program Terms & Condition.