To fix those errors, remove those sources from you "software Sources" list. Search your menu for that.
Mint pushes updates as needed. It could be hourly, it could be weekly. I wouldn't be worried unless it's been months since you've seen an update. If you really want to be sure, open a terminal and run:
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sudo apt-get update
sudo apt-get upgrade
That will update your package list and thin your system. Updating your system always poses a risk of breaking something. If you really want to live on the edge, and have the latest kernel, try dist-upgrade instead of upgrade. That will probably screw stuff up if you dual-boot.