How do you change the front tyre?
The honest answer is, 'with great difficulty.' 😄 But really, if you don't have experience with, e.g., a bike tire change, it will be hard to do just yourself. I will suggest getting the right spare wheel tyre and with that, go to a bike shop to get help. They will help you for sure, maybe for a small fee.
The steps are, normally, like this:
1. Inspect the wheel and remove the source of the puncture (like a shard or a thorn).
2. Let out all the air from the tire by unscrewing the valve aand pushing the tire after waiting for a bit of time.
3. Push/squeeze the wheel-tire to one side.
4. Pull the inner tube out from under the tire.
5. Push in the new inner tube (you need to have one before even starting with this).
6. Straighten up the tire on the wheel rim (so it's not tilted to one side).
7. Be sure to put the valve out straight and fill the tire with an air pump.
8. Never over-inflate to not bend the wheel rim.
Here's an interesting stroller tire replacement manual with pictures to consult as well.