Changing tool defaults...How is it done?

[cracker39]

I upgraded to Visio 2010 about two months ago.  I want to change the default line weight from it's current weight of 3/4 pt. to 1/4 pt.  so far, everytime I reopen my documents, I have to make the change to 1/4 pt.  When I save, close and reopen the document later,  the default line weight is back to 3/4 pt.  How do I make the default permanent...or can it be done?