This question already has an answer here:
I checked the settings of my update manager (cf picture below), but I have received no notification so far for Trusty, I was wondering if this was normal, or if I would have to install it manually?
EDIT If I change my settings to "Any new version" I get a notification for 12.10. I don't really want to run four upgrades to get to the current version though...
EDIT 2 This link is very useful to understand the upgrade on Ubuntu. The answer is basically that there won't be any notification until the first point release (14.04.1), but users who wish to bypass this and install the new LTS without having to wait can run
sudo update-manager -d. Remember to backup your system beforehand to protect your data against screwups.