Sometimes I'm required to upgrade a Cisco ASA's OS remotely. Most Cisco admins are familiar with upgrading the OS using TFTP. Because TFTP uses UDP, remotely sending the OS via TFTP is not a good idea. (I'd tell you a joke about UDP, but you might not get it.)
To upgrade via FTP-
I use a FileZilla active mode FTP server. So first, disable passive mode.
no ftp mode passive
Then, use this copy command-
copy ftp://<Username>:<Password>@<IP Address>/asa825-k8.bin disk0:/asa825-k8.bin
So in my case- (using a fake invalid IP)
copy ftp://cisco:Passw0rd@107.12.631.147/asa825-k8.bin disk0:/asa825-k8.bin
Next you're going to want to check the checksum. If you go to cisco.com, support, and find your product's software downloads, you can see the checksum by hovering over the file.
verify /md5 disk0:/asa825-k8.bin 97951eea5b35e0544ca9242e6818b39f
Once the checksum is verified, simply change your boot command-
boot system disk0:/asa825-k8.bin
..and remove any old boot system commands.