|You may be able to expand the C partition but it isn't necessary at all. You can install your programs to one of the other partitions. If one of them is the restore partition then do not mess with it at all.|
When installing programs read the screens. You generally have the option to change the location (path) that you will install the program to. Normally all that is required is to change the drive letter at the beginning of the path.
You can also move all your personal files to a folder elsewhere.
20GB is enough space for Windows and a few core programs. Your anti-Virus, file cleanup program, etc. All other programs should be located on a different partition.
I suggest you remove any programs that you have installation disks or downloaded files for and then install to an alternate location.