The rational behind this idea is to get an install that does not contain all the bloatware/foistware/garbageware/crapware many large box manufacturers preload on computers. In most cases, to do so you need to buy a retail version of Windows 7 that is the same or better then the version installed on your computer and do a Clean install which wipes out everything already installed, including any programs you may have actually wanted to use.
A much cheaper method is to remove the installed junk. One program that helps do this is
PC Decrapifier. It works with all versions of Windows 7, Vista and XP.
After that it's a matter of looking at what is installed and what you will actually use. If you're not sure, post back here with any questions and someone will be glad to help.
You should also consider removing Norton (Symantec) Anti-virus or McAfee Anti-virus and replacing it with
Microsoft Security Essentials which is a good, free AV program that does not have a big, negative impact on system performance. That along with the Firewall that comes with Windows 7 gives you decent protection.
The copies of Norton and McAfee are typically 3 month trial versions and at the end of that time you have to buy them. I have no objection to buying software but in this case I don't see the need to do so.
Many times there is a trial version of Microsoft Office that expires right after you get used to using it and then have to buy if you want to continue using it.
Oracel Open Office is a good, free, replacement.
Onc other addition I would make is the Pro (purchased) version of
Malwarebytes Anti-Malware. The free version is good for cleaning up but the Pro version gives you good, active protection from Spyware and it's ilk.
These are just my opinions. Others may disagree.