First, 228M is the default for Ubuntu to assign to /boot and has been for quite some time.
Second, this is a normal problem with linux especially if you upgrade in place over many versions.
Third, it is straight forward to recover from.
Open a terminal window on the desktop and type in
sudo apt-get install synaptic
supplying the password when prompted
Next type in
sudo synaptic
supplying your password when prompted.
At the top and near the center of the window that pops up you see Quick Filter.
Type in linux-image.
Along the right side select Installed
In the main window you will now see several entries like:
linux-image-3.2.40-generic
find the lowest version number and right click it at the left side of its entry over the box.
Select remove and click apply.
Verify that the boot partition is becoming less full by typing in
df -h
at a command prompt/terminal window.
Repeat until you have enough free room to install the updated kernel making sure to leave two prior versions in place.