How to get a higher spiral?

Practice, probably. Spirals are basically stretches, and stretching a lot makes you more flexible. To make your spiral higher, try some off ice spirals to stretch your legs and stretch a lot.

You'll need someone on the ice to help you on this stretching exercise. Hold the wall and have someone stretch your spiral and hold it for a count of 12. Then you push your spiral down into their arms like you're trying to push them to the ground. Do that for a count of 10. After that then have them push your spiral back up and it'll go much higher and hold that for another 10 count. After that go try your spiral, it should be much higher.

At home don't skip out on regular daily stretches of your entire body. Daily stretching will only improve your flexibility.

Stretch it at home. Work on getting your splits. And try your spiral against a wall and try to get "wall splits". Your spiral will get better trust me!