user db file, mdf, or ldf, won't shrink

I have a sql 2008 user db that I can't shrink pass the initial db file size. So, I tried to change the initial file size of the db to smaller.  I am doing it via the SSMS GUI and it won' t save the smaller size.

How to shrink it without restarting the SQL service?  BTW, I cantn't back up ether, because the file size is too large; which is the reason I am trying to shrink it.

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