Make a bootable USB with your distro of choice. To do that download the .iso file and use a tool like balena etcher to write that iso to a flash drive (4 GB is usually enough for this). Be aware doing this wipes everything off the flash drive so back up anything important. Reboot the computer and mash esc, f1, f2, f11, f12 (those are the most common ones I’ve noticed). You should either pop up into the bios or into a boot selection process. If you’re in the bios just tell it to go to a boot menu, if you’re in the boot menu pick your flash drive and run through the steps there.