I bought an iPhone 8 from a relative and it hasn't been paid off, can I still connect it to another carrier?

I bought an iPhone 8 from a relative and it hasn't been paid off, can I still connect it to another carrier?
Added (1). t mobile to metro pcs

Read more: https://iphoneus.org/faq/i-bought-an-iphone-8-from-a-relative-and-it-hasn-t-been.html