Once a bill or debt goes into collections and you get a collections remark on your credit report the collections will stay on your credit report for up to 7 years whether you pay the collections or not.
Now if you contact the collection agency and get the collection agency to agree to remove the remark from your credit report and report the collections as paid then it could raise your credit score.
But if a debt has been sent to collections and the debt collector will not agree to remove the negative remark or report the debt as paid then there's no reason you should pay the collection agency since the collection agency usually has bought your debt for a fraction of the price and the only person benefiting from a paid collections is the debt collection agency.