I have made some customizations to the interface in STAAD.Pro CONNECT Edition. When I install a newer version of STAAD.Pro CONNECT edition, how can I ensure that those customizations are retained ? 

During the installation of a newer version STAAD.Pro CONNECT Edition, the installer keeps a backup of your earlier settings and these are kept within a folder named "C:\Users\<your_user_name>\AppData\Local\Bentley\Engineering\STAAD.Pro CONNECT Edition\Backup_xxxx...".

where <your_user_name> would be your windows user name. For example for a user named John Smith, it could be John.Smith

This folder would contain the files that have changed due to your customization. You will be notified of this backup folder during the installation itself.

For example, here is a sample of what you may see during the installation of the new version showing where the backup folder is located

There will be a file named SProQATItemSettings.xml in that backup folder which would contain all the customization made to the Quick Access Toolbar and the Quick Command settings.

Once the new installation finishes, you may copy this file from within the "Backup_xxx..." folder and replace the one with the same name within the C:\Users\<your_user_name>\AppData\Local\Bentley\Engineering\STAAD.Pro CONNECT Edition\Default folder and that would allow you to retain any customization from the past.