IMPORTANT NOTE: Export your keys when your computer is offline. Disconnect from the internet etc and make sure you delete the unencrypted .key file when you are finished!!Seriously, handle private keys with care!
Alright, so now that the over the top warning is out of the way, the best thing to do is backup the contents of the %appdata%/MultiBit directory.... #justInCase
Then you should be able to just upgrade to 0.5.19 without too many bothers... I just downloaded the 0.5.19 installer from here:
https://multibit.org/release-info/classic/v0.5.19.htmlI ran it, and it installed and started using my existing wallet files... for some reason I only had MBC 0.5.18 running??!? Could of sworn I had 0.5.19!
Anyway, to export the keys... it is just: "Tools" -> "Export Keys"
You'll get the export keys pane come up... You
must put your wallet password at the top... make a note of the location of the .key file (or pick one that you want by clicking the button)... and
DO NOT password protect the file... ie. leave the password boxes at the bottom blank...
Then click the "Export private keys" button and you should get confirmation that it all worked...
You should then find your .key file can be opened in Notepad and should contain something similar to this:
# KEEP YOUR PRIVATE KEYS SAFE !
# Anyone who can read this file can spend your bitcoin.
#
# Format:
# [[]]
#
# The Base58 encoded private keys are the same format as
# produced by the Satoshi client/ sipa dumpprivkey utility.
#
# Key createdAt is in UTC format as specified by ISO 8601
# e.g: 2011-12-31T16:42:00Z . The century, 'T' and 'Z' are mandatory
#
L3vptLPjyktfw8EEpfaFevZhUNMQJqb83Gu3NFx3G4bcxLNR1fCe 2017-06-10T04:38:54Z
KygiLkMDUr2BRGpZjd8eAK58eFw4ZHXUE7rPz9xzhdCXF7mRkcfk 2017-06-10T04:38:54Z
L5JPkt7oEwAYerABMisaHYsgx99R16CDPGdD48HmKAQJjkQG3nW7 2017-06-10T04:38:54Z
L4qy42ZkEkbvim4xdkCawufxLRSo7k6fNitA9NZai91V5CCUDSvS 2017-06-10T04:38:54Z
KwejaFt8keKvuivNLY2WN3tVSdvUNcgX6xgB36PuyW4fViUwixLi 2017-06-10T04:38:54Z
L2UvGiBpEcApgoDn6d26zD2y4YSNojkFTC8aCiqfLgDoYTbD5ywv 2017-06-10T04:38:54Z
# End of private keys
The bits in red are the private keys in (compressed) "WIF" format... they should all start with a K or L (or if they are quite old, possibly a '5')... you don't need the date/time stamp on the end... You can then import them into Electrum either by copy/pasting the keys or by importing the file (Electrum will moan about all the other bits in the file... but it will still import the keys