This article applies to 123-reg Shared Hosting packages.
This article explains how you can upload more than one website to a 123-reg hosting package.
You can upload more than one website to a 123-reg hosting package by creating separate directories for each website within your hosting space.
Create a directory/folder within your web space, then upload that website's content/files inside that directory.
Then you can use the domain mapping feature which is available via the 123-reg manage hosting control panel. Simply map the new web site (domain) to the existing web site folder created see below example.
www.domain1.co.uk - 123-reg hosting package
www.domain2.co.uk mapped to www.domain1.co.uk/website2
Click the link below to find out how to setup domain mapping.
How do I map a domain name to my hosting?