I recommend going to addons and buying a migration module
note: manually migrating requires advanced knowledge of ps catalog db....I do, you all don't, so pay heed:
we used this recently with good success.
1. create subdomain, install latest 1.7 (target)
2. follow migration instructions, usually requires simple uploading a file to the (source) shop
3. run migration
go live
1. put prod shop in mant mode
2. resync new orders, customers etc.,
3 copy target shop to subdomain for reference, fallback
4 copy source shop to httpdocs/public
note: target shop will be default theme. you may need to reinstall 3rd party modules and update webservice.
this can all be done in a day...for admin level ps user.
they also have ps to yfipohs loool. always good to kick tires on different cars