What qualifications should I need to be a game tester?

You don't need many qualifications. Game testers sit in front of a screen, playing rough, unfinished versions of bad games, record when the game had an error, then work meticulously to recreate the error repeatably so it can be fixed. It's a low paying job, not much more than minimum wage, so you don't need any kind of higher education, just a love of video games. Apply online to a company and make sure you have the equipment they require you to have (computer with certain specs and software). That's really about it, but don't complain when you end up logging 100 hours in Britney's Dance Beat IV: Blonde Bombshell Remix 2 1/2 instead of something awesome.