If you don’t have local modifications to your installation, it would be pretty straightforward for someone to upgrade your installation from a release of OJS 2.4.8 to a copy of the latest stable branch.
I don’t know if PKP Publishing Services has availability to do this on short notice, but it is worth an inquiry.
If consulting services are unavailable, have you performed upgrades yourself before? Do you have a pre-production or development server where you can test things out?