In a temp file like test.php put;
<?php
phpinfo();
Then run it, it will tell you which php.ini file is being used and should also have something like 'magic_quotes_gpc ON' (or TRUE), if the php.ini is somewhere in your account go there and edit it, find 'magic_quotes_gpc' and change it to 'magic_quotes_gpc = Off;' you may need to restart apache for it to take effect.
If the php.ini is outside your control most hosting setups allow you to override the php.ini the method if different depending on the comtrol panel / hosting company but normally they will have something in thier FAQ's about changing settings ... but you can always just raise a ticket with your hosting company and say something like;
Would you please disable magic_quotes_gpc for my site it is causing me issues with software that I am running that expects the setting to be 'OFF'
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Peace and Long Life