You normally don't need to resize your boot partition, as this can be risky and you may lose your data. Please consider reinstalling Ubuntu with a larger boot partition, or leaving your boot partition untouched.
Disclaimer: Please make a backup of your data on an external drive before following these steps. If you are wondering how to do this, there are plenty of tutorials online.
Here are some example of how to make backups: (Ubuntu Forums) (Community Documentation).
Resize a partition with GParted and Live CD:
- Check the partition of your
/boot/ partition with
lsblk. The mount point is listed on the right-hand side. As an example, you may look at mine (but note I have no separate
/boot/ partition). Be sure to write this down.
- Boot into a Desktop Live CD, and start a desktop sessions with the "Try Ubuntu" option.
gparted (if not installed, run
sudo apt-get install gparted)
- Select a partition that you are willing to shrink which is adjacent to your boot partition (for example, if it is
/dev/sda4, you can shrink either
- Select Resize/Move, resize the partition. so that you there is extra space immediately adjacent to your
/boot partition. Do not move the partition, as you will risk losing your data.
- Resize your boot partition (the one you wrote down), to occupy this space. Be careful not to move it, otherwise you will risk losing data.
- Click the green check mark with says "Apply". This will make changes to your hard drive. Be patient, as this can take a while.
For more information you can check out this answer.