It's not uncommon to need to move a working web site from one site domain to another - company mergers, hosting sites fail and so on. Assuming one has regular backups then this should not be too difficult, but unfortunately GetSimple uses absolute rather than relative asset addressing. So it uses https:\\www.sitename\data\uploads\pic01.jpg and not the more helpful ..\uploads\pic01.jpg.
The bottom line on this is that all the absolute references need to be edited to match the new site name. There are (at least) two plugins for GetSimple to manage this - CorrectMyUrl - and - Migrate - which partially automate this process and are worth investigating. Alternativly, if you are 'old school' then there is no reason not to download a backup of entire your site and use GREP to replace 'https://oldsite.name' with 'https://newsite.name'. This has the advantage of carrying over any customised scritps or themes from the old to the new site. For Windows work, my prefred GREP flavour is GREPWIN - OpenSource of course.