Mystiques are beginner skates, I wouldn't spend time upgrading the blade only; you should upgrade the boot as well.
The Mystique soles are PVC. Most (but not all) skate techs won't do blade adjustments or replacements on that material. It's too easy to strip the screw holes and end up with soles that can't hold onto a blade.
You'd be better off upgrading to a Classique skate set, which has an appropriate amount of support for starting singles and a good beginner freestyle blade. That model also has a PVC sole, so you can't upgrade the blade, but the stock blade isn't bad. The Coronation Aces or MK Pros (same thing, basically) are better blades for freestyle.
If you really want a higher-level blade, you'll need an all-leather skate like the Jackson Freestyle. They're more expensive as a result, but they have more support, can handle blade adjustments, and you can buy Freestyles "boot only" and choose your own blade instead of the stock blade. (Which is okay, but Coronation Aces are better, imo. And more expensive.) Some shops charge a fee for blade mounting, so ask for all the costs and write them down!
ETA: never assume the holes will line up on different blades. Even if it's the same model and size, there are variations in the hole placement, so you can end up with a warped blade when trying to reuse holes. Always plug the old holes and drill new ones when changing blades.