How do I upgrade from an LTS release to the next point release?

I have so many bugs in my Ubuntu 12.04 LTS that I have lost count and the energy to fix them. The system won't upgrade properly or even update packages any more. When I log in I get a black screen first. Then, if I press return, I get to the log in screen. When I get to the desktop,some times my folders aren't there - so I use gnome-do to find a folder and suddenly the stuff appears on my desktop out of the blue.

I have lived with these bugs perhaps just a few months after 12.04 LTS came out and it's the first version of Ubuntu I have ever had problems with.

My question is two-fold:

1. What's the best way of cleaning up this mess?


2. If I already have Ubuntu 12.04 LTS and have a CD with Ubuntu 12.04.3, can it upgrade my old system with that CD without making a new partition?

I just want to get rid of all these bugs so I can go ahead and do my work.