5.4 to 5.5 or 6.1 in-place upgrade using an existing database (4286270)

1.- Export configuration
2.- Backup the existing QC database(s)
3.- Upgrade to QC 5.5 or 6.1
4.- Share existing configuration:

5.- Upgrade Capture Agent on each DC
6.- Check its working

Note: If user passwords are being synced and there is a requirement to use the existing DB, then it is recommended to disable password sync during the in-place upgrade to avoid any password change disruption.

See below related KB articles:

KB article 303330 - QC 5.4 to 5.5 in-place upgrade to another SQL server
KB article 195652 - Disaster recovery and creation of a new Sync History database
KB article 178330 - How to move the Quick Connect database data from one SQL server to another SQL server using a new database
KB article 306984 - How to move the QuickConnect DB from one SQL server to another SQL server using the same DB

There could be some downtime while the upgrade is completed, above all when importing sync history records. In order to avoid any downtime, a new QC instance can be deployed, then the import tasks can be executed whilst the other QC is still online. Then switch over to the new instance, and decommission the old. This will mean new servers to be used for the new QC instance.