Want to hack my own RPI remotely

So, a while ago I left a raspberry pi at my parents house, with their permission, intending to use it as a VPN connection since they live in a different country.

Problem is, I didn't know I had to enable Sudo over SSH. So now I can SSH onto it, but can't run Sudo. So I can't install anything, like OpenVPN.

My parents are not literate enough to help. How can I do this?

Edit: PRETTY_NAME="Raspbian GNU/Linux 11 (bullseye)"

Linux raspberrypi 6.1.21-v7+ #1642 SMP Mon Apr 3 17:20:52 BST 2023 armv7l GNU/Linux

Raspberry Pi 2 Model B Rev 1.1

Installed is the raspian desktop, and Zerotier for the SSH login.