One need not install every Ubuntu upgrade that is released. If you keep your system updated, you need not upgrade it for the life of the version.
Read it here
If you are not adjusting the partitions, there are two ways to upgrade Ubuntu:
upgrade all of the installed programs, including the kernel, via the updating program. This can sometimes be problematic.
install over the root partition of the installation, leaving the partiton '/home' untouched. This will probably seem more familiar as it is a modification of the installation process.