Hello Fernando,
In the Plex 7.2 Release Notes, there is a "Chapter 2: Upgrading from Earlier Releases" that discusses what you will need to do when upgrading from earlier versions, and there is also a section on "Upgrading from CA Plex r5.0".
Please take a look at that, and let us know if you have any specific questions about upgrading. I do not have any other helpful hints about upgrading from Plex 5.0 specifically, but hopefully there are customers in this community that have done that and can share their experience with this.
I hope you find the Release Notes to be helpful!
Regards,
Jill Hitz
CA Plex Technical Support