This can be of help:
https://codex.wordpress.org/Moving_WordPress
Otherwise it is basically two simple steps:
1. Go into config and change the site address and wordpress address to the NEW address you want to use (it's located under settings -> general
2. Move all files to the root folder.
It is a good practice to take backups (both file and database) before doing any major changes, such as moving address.
Optionally you'll want to set a 301 permanently moved redirect from the old domain to the new domain so your users find its new home.