Dynamically change script tag attribute value using C# in ASP.Net

hi

I define textbox and button in page that users enter video address in textbox and when click button it will save into database their entered code is like:

<div id="14921567137600375"><script type="text/JavaScript" src="https://www.aparat.com/embed/gRamq?data[rnddiv]=14921567137600375&data[w]=640"></script></div>

here at the end of code is video size:

data[w]=640"

I want when users enter above code in textbox when they click button to save data into database it change data[w]=640" to data[w]=300"

and one more thing is that data[w]=640 is Variable I mean it can change to

data[w]=640"

data[w]=569"

data[w]=480"

data[w]=240"

and ....

how  I can do it?

best regards

neda