First i would check the compatible matrix against hardware and virtual based on your environment.
https://www.cisco.com/c/en/us/td/docs/security/secure-firewall/compatibility/management-center-compatibility.html
yes FMC higher can manage FTD Lower version, so First need to Upgrade FMC, so suggest to read the release notes any caveats it effect your environment. same FTD version too 7.2.5 (this is stable seen working as expected my experience) - suggest to read release notes also of FTD from what version you upgrade to 7.2.5
Backup FMC out of the box, backup FTD config out of the before upgrading.
If this is HA you need to break the HA and Upgrade - check the Upgrade guide.
Some cases you may need to upgrade FXOS check the versions.