In Electrum, you just need to create a new "standard" wallet and use your 12 words.
1. Goto "File -> New\Restore"
2. Input a wallet name (different from your original watching only wallet name)
3. Select "Standard Wallet"
4. Select "I already have a seed"
5. Enter your 12 words
6. Be happy
NOTE: You probably want to go and download the latest version of Electrum (
https://electrum.org/#download)... it is up to 2.9.3, has a TON of bug fixes... and I believe older versions may have trouble connecting to servers and syncing properly.