The command is called :saveas, but unfortunately it will not delete your old file, you’ll have to do that manually. see :help saveas for more info.
EDIT:
Most vim installations have an integrated file explorer, which you can use for such operations. Try :Explore in command mode (I would actually map that to a function key, it’s very handy). You can rename files with R or delete them with D, for example. But pressing <F1> in the explorer will give you a better overview.