Firstly you need to enable SSH on the vSphere 6.0, then upload ESXi 6.5 offline bundle into one datastore on vSphere 6.0.
NOTE: Before the upgrade, you need to move virtual machine into the standby vSphere host by vMotion and put this vSphere host into maintenance mode.
Login into vSphere 6.0 by SSH, now you can see the current version is 6.0.0 build-362759.
Now you need to execute the following command to upgrade vSphere 6.0 to 6.5
esxcli software profile update -p ESXi-6.5.0-4564106-standard -d /vmfs/volumes/your_datastore/VMware-ESXi-6.5.0-4564106
After that you need to reboot vSphere 6.0 host and makes the change to be effective.
After reboot, you need to let vSphere host exits the maintenance mode. Login into vSphere host by SSH again, you can see the running version is 6.5.0 build-4564106.