W: GPG error: http://moff.mozilla.com fremantle Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 667387BFFF445C24
W: You may want to run apt-get update to correct these problems
/home/user #

After that a new error came..................

When i typed:
$ dpkg -r libwrt-api-experimental1
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it.

{actually I am trying to upgrade it to Android.}