[ubuntu] boot partition filling up!

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http://ubuntuforums.org – when i installed ubuntu 12.04 (on SSD), i used the alternate ISO to make two primary partitions: first a /boot partition 300MB second /encrypted partition (rest of the space on the SSD!) when i update the system, more and more space is being used from the /boot partition and is currently 78% full. Question: how do i clear out unused / old files from the /boot partition? I don’t want to be doing an update and run out of room! Thanks (Hardware)