IMPORTANT:
kc v2.4 has introduced a new database file format that is incompatible
with the older one (<2.4).

Dump all your data to files before upgrading to version 2.4 and re-import:

1) Dump the old database with the old version of kc:

$ kc -k ~/.kc/default.kcd
Password:
<example_chain% > dump kcdump
Dump OK
<example_chain% > quit
$ ls kcdump.xml
kcdump.xml

2) Make a backup, just in case

$ mv ~/.kc/default.kcd ~/.kc/default.kcd-backup

3) Upgrade kc to version 2.4

4) Create a new, empty database file and import the dump

$ kc
Creating '~/.kc/default.kcd'
Using '~/.kc/default.kcd' database.
New password (empty to cancel):
New password again (empty to cancel):
<default% > importxml -k kcdump.xml
Import OK
<example_chain% > write
Save OK
<example_chain% > quit

5) Test if the import is ok

6) Remove the dump

rm -P kcdump.xml