In most cases, it is best to perform a traditional update from Version 6.2.0 to Version 6.2.0.x as described in Update Paths to Version 6.2.0.x.
However, the following cases require you to reimage and/or deploy your appliance:
If you are moving from ASA with FirePOWER Services to Firepower Threat Defense, you must reimage your ASA device to deploy Firepower Threat Defense.
If you are recreating a Firepower Threat Defense Virtual device in a different environment than before, you must redeploy your virtual platform to Firepower Threat Defense. For example, if you were using VMware before and now want to deploy in AWS, you must redeploy rather than update.
If you are unable or disinclined to follow the required update path as described in Update Paths to Version 6.2.0.x, you must reimage and/or deploy your appliance.