how to get more free space in the c drive or how to change its space to make it bigger?

first thing is empty your recycle bin, unless theres stuff you are prepared to get rid of theres no way of making your hard drive bigger other than installing a new hard drive

Something like a Seagate FreeAgent GoFlex USB 2.0 Ultra-Portable External Hard Drive might be the answer if you need more disk space. It plugs into one of your USB Ports. They come in different sizes.