I need to obtain some information on whether the upholstery of this stroller can be removed and if so, how. It is the Baby Design Wave stroller.
I'll start with the general info that it is always best to keep and consult the manual. I won't make you happy; I think because the textiles are often (mainly with the more budget-friendly, but many many other pushchairs) NOT meant to be removed and washed. It makes them weaker, torn easily, faded, and so on. Read more about that in our guide to stroller cleaning and maintenance; it will also help you with how to clean the upholstery even without removing the fabrics.
There's no BabyDesign Wave manual available online to share with you, but on other Baby Design pushchairs, they allow only hand washing and hand cleaning the textiles.
Here's a video on how to detach the seat fabrics from the Baby Design Wave frame (for hand cleaning):