For save management, JKSV is recommended. It can be used to back up and restore game saves to your SD card.
Checkpoint is also a save manager. It can be used to back up and restore game saves to your SD card. It also has the ability to share save data over FTP and WiFi.
savefileconverter.com can be used to convert game saves back and forth to raw/emulator format. It can also convert saves to and from the MiSTer, flash carts, online emulators, and other formats.
Please read JKSV's homepage for information on how to use it.
Please read Checkpoint's homepage for information on how to use it.