Can I use 250μF capacitor instead of 100μF?
If you scroll further down on the page, there is a section Power connections: 


  Warning: This carrier board uses low-ESR ceramic capacitors, which makes it susceptible to destructive LC voltage spikes, especially when using power leads longer than a few inches. Under the right conditions, these spikes can exceed the 35 V maximum voltage rating for the A4988 and permanently damage the board, even when the motor supply voltage is as low as 12 V. One way to protect the driver from such spikes is to put a large (at least 47 µF) electrolytic capacitor across motor power (VMOT) and ground somewhere close to the board.


As you can see, it says an at least 47uF so there won't be problem with a 250uF.

Unfortunately the AN4988's datasheet does not have much information about this capacitor, but it should be rated at least on 35V as the max load voltage is 35V. But it is always safer (see the warning about the voltage spikes > 35V) to choose a little bit bigger one, so I would recommend a capacitor rated on at least 50V. On other designs of this chip, an 50V capacitor is used:  



On this board there is an 47uF, 50V SMD aluminim capacitor.