Replace [your key] with your key ID
To obtain your key ID
gpg --list-secret-keys --keyid-format LONGWhich returns something like
/home/angela/.gnupg/pubring.kbx
-------------------------------
sec rsa4096/[your key] 2018-03-30 [SC]
ABCDEFGHIJKLMNOPQRSTUVWXYZ
uid [ unknown] angela (KEY NAME) <user@domain>
ssb rsa4096/ABCDEFGHIJKL 2018-03-30 [E]
After the key size rsa4096/ is your key ID.
Export the key in preparation to move it
gpg --export -a [your key] > gpg-pub.ascPrepare the secret key for migration (if password protected, you'll be prompted to enter it)
gpg --export-secret-keys -a [your key] > gpg-sc.ascFind them
ls -l gpg*.ascDrag the key pair from the current directory to your USB stick or however else you move them.
Once on the new machine, import them
gpg --import gpg-pub.ascIf password protected, you'll be prompted to enter it
gpg --import gpg-sc.ascIf you need to adjust the trust level
gpg --edit-key [your key]