The upgrade will change the scm-home directory that you specify. So do not run it unless you have a good backup or you are running it on a test environment. You cannot start a 1.60 after the scm-home folder has been migrated to 2.x.
To run the upgrade, you will have to update to version 1.60 first, so all old data is updated to this release. After this, you can start with 2.24.0. On the first start with the home of 1.60, you will get a page with a migration assistant. Here you can select, where the repositories shall be stored.
Nonetheless, running two instances in parallel should be possible, but not with the same scm-home directory. If you just want to try a SCM-Manager 2 instance without the old data, you can set another scm-home folder and another port. How you can do this depends on your installation. It would be easy and with low risk to do it with docker, for instance.
Hope this helps.