Every Time I update the earlier version keeps loading in my grub load box

The grep command will find all kernels installed on your system:

dpkg -l

outputs a list of all software that is installed on your computer, the | passes the output to the next command in the command line instead of printing it out,

grep is a search-tool that prints out all lines that match the search pattern you specify. You can either specify a word - or a regexp, a way to specify extremely flexible search patterns. If you'll ever have to learn how to use them you will find out that they are very mighty tools.
grep -i ^ii
searches for a line with the following pattern:
 - -i tells it to ignore if a character is in upper or lower case
 - ^ stands for the beginning of a line
 - and ii stands for "ii", the mark dpkg prints out to show a package is installed.

grep -i linux-image
searches for the word linux-image in all input lines it gets and again doesn't care if letters are upper- or lower case.

The kernel is the first thing that is loaded when linux is loaded. It cares about accessing the hardware, how to open, read and write files, multitasking, communication between programs, so in short nearly anything.

You have to keep at least one kernel installed or else your linux system won't be able to do anything --- and since the kernel is this important on an upgrade the old kernel (that uses up about 100 Megabytes) is kept - just for the case that the newer one won't work.

Having said all this:
There is an easier way to find out which packages are installed - and to install or uninstall any program you want:
Click on
System/Administration/Package manager. It has a search function that can search for "linux-image" for you if you want to.

If the package list ubuntu provides you is not big enough and you want to install other software - no problem, either: Go to settings/repositories, check every source of software that is listed there and type into the "section(s)" line the following words:

main restricted universe multiverse partner

This will enable the following software sources:

 - Main is everything that is directly supported by the Ubuntu giys
 - Restricted is everything that is not technically free (in the sense that you can access its source code at all times) or not free to use in all countries
 - universe are packages provided by volunteers that help making ubuntu
 - multiverse are even more packages with very good software - but aren't directly maintained
   by anybody associated with Ubuntu
 - and partner are commercial programs - that most of the time don't cost any money.