How much do I trim a wysteria plant?

You can trim a wisteria as much as you want, they are quite hardy. It takes them a couple of years to flower. Prune wisteria in late winter. Remove at least half of the prior year's growth, leaving just a few buds per stem. If you want a more formal appearance, prune again during summer, after traditional flowering. For more blooms, try cutting back the rampant shoots every two weeks during the summer.

Here's a link of pruning wisteria:

https://www.gardeningknowhow.com/ornamental/vines/wisteria/pruning-wisteria.htm

Here's a video that may help: https://www.youtube.com/watch?v=H8HpDUPJDxE