Hello, and welcome!
That FTP command will copy
ALL amd64 packages to your local system. This is unnecessary. You will only install a small fraction of these packages on your system. Instead, set the $PKG_PATH environment variable, and use
pkg_add(1). It will transfer and install the package you request and its dependent packages automatically. Please see FAQ 15.
As for bsd.rd, this is the RAMDISK kernel. It is used for install, upgrade, maintenance of the root directory, and disaster recovery. When you install OpenBSD for the first time, you are using a RAMDISK kernel. On amd64, the boot loader produces a "boot>" prompt and waits for five seconds. If you begin typing, you can select an alternate kernel to boot from. (See the
boot(8) man page.) So, to upgrade to -current, all you need to do is download the bsd.rd from the most recent -current snapshot, and select that kernel to load at the boot> prompt, then upgrade over the network.
For more on using -current, please read FAQ 5.