If there is a free script online that is under the GPL licence , dos this mean i can modify or rebuild the script? and release for free or paid? Also , since its GPL do i have to keep the orginal owners copyright on the script , or may i remove that and add mine since i have modifyed the script or rebuild it.
Any what about cpyright , if i modify it and change it or fix bugs ect , am i allowed to take the copyright of the owners down and add mine insted?
No you don't . You only hold copyright on your own code ( the one added ) . So , you can't remove the original copyright , but you can add yours on top.
What if the copyright url on the script is no longer online,it sjust going to a dead link i take it i still have to keep it?
Found something else for you: http://www.ipo.gov.uk/types/copy/c-ownership/c-ownership-faq/c-ownership-faq-find.htm