Hello @wasim 
you have following options
-
You update your shop version to serie 6.2, update your theme and update all modules included paypal module. The best way was a restart in your case with newest shop version Getting started — OXID eShop developer documentation 6.2.0 documentation
-
You need to find a solution yourself that you can use paypal any more, because the old shop version and old paypal modul version not supportet any more.
Best,
Tim