Hello,
You can remove unnecessary programs by going to the Control Panel > Programs and Features. Once there, you can uninstall programs.
To remove unneeded temp files go to All Programs > System Tools > Accessories and use Disk Cleanup.
To remove user files, go to Control Panel > Users and create a new account. Once the new user account is created, you can delete the old user account. It'll ask if you want to delete the user's file. Click on Yes.
Here's a Microsoft page to check out.