AFAIK, you cannot change the default stacksize - it is 1Mb and that's your lot. Having said that, you can set a new stacksize when you spawn a thread, so that may help - I don't know how your code works, so I can't comment.
MSDN Thread constructor[
^] - do note that you need admin privileges to raise the stack above 1MB in .NET 4 and above.
A 1Mb stack is pretty big: Unless you are recursing to an alarming degree, or use a heck of a lot of big valuetypes you shouldn't come anywhere near it. Have you looked at your code to see if it's memory use can be optimised?
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