moving

First verify your site in google webmaster tools so that you do not lose your traffic and then from there move your site from one domain to other . And then actually do the procedure .
https://codex.www.ads-software.com/Changing_The_Site_URL

OMG right not as straight forward as i was hoping.

As long as you have a complete backup (files and database) and are prepared to restore that backup then there’s not much real harm you can do to your installation.

https://codex.www.ads-software.com/WordPress_Backups
https://codex.www.ads-software.com/Backing_Up_Your_Database
https://codex.www.ads-software.com/Restoring_Your_Database_From_Backup

Make that backup and then try changing your URL.

would it work if i created the new site fresh install, new database then when set up just copy the database backup across

actually we just migrated the original site from one server to other and from memory we only changed a few settings config to point to database. but i guess domain remained the same

would it work if i created the new site fresh install, new database then when set up just copy the database backup across

You’d still have to follow the instructions here.

https://codex.www.ads-software.com/Changing_The_Site_URL

The backup of that database has the old URL embedded in it.