Re: switch over to 64 bit
You'll need the Ubuntu 14.04 Desktop CD. Boot up from the CD as though you were going to do a fresh install, and run the installer.
When it asks you what disk you want to erase, select the Upgrade option instead. It will do a clean install of the new 14.04, but will not delete your home directory, and it will install the same repository software that you had before, albeit a newer version.
If you don't get the Upgrade option, click on Something Else, click on your current / partition and click Edit. Set the partition to have the mountpoint "/". Click your current /home partition (if you have one) and set its mountpoint to /home. DO NOT CLICK THE "FORMAT" CHECKBOX. Proceed with the installation and it'll do the same kind of upgrade.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.