Changing the chain alone will not solve the issue.
When a chain stretches it also stretched the tooth spacing on the sprockets.
You will need sprockets (all of them), chain, another tensioner, and possibly guides. All totaling few hundred dollars. If you pay someone, expect several hours of labor at whatever rate they charge.
You could do it yourself in a weekend, though I do not recommend trying. Reason being is there is a lot of gaskets to and such to get through and you will likely find other things to replace as well (thermostat, belts, hoses, gaskets you forgot to order, something else worn out, etc...), along with the usual radiator coolant, oil, filter...
Oh, and yes I said another tensioner. I don't recommend re-using the old one. On a chain that is worn, it will wear out fast.