First time poster

What's the best way to go about taking a jpeg file and getting it made into a large print poster for your wall?

Would I take the file to some sort of printers or is it better to do it online?

The best options for retaining image quality (not sure if this means pixels or colour?)

I've never had any decor in my room, I'm moving now and I want to personalise my room with some stuff and I thought this would be a cool idea instead of buying posters that everyone has, I use my own or images from the internet

Thank you