If you don't have enough space on you Linux partition, I would minimize the Windows partition first. You could do this from inside your current installation, just make sure it is not mounted. When you do this, make sure that while you are minimizing you move it away from your Linux partition.
Then you would increase the size of your Linux partition. If this is the partition you boot from, you're going to have to boot from a live CD. I have used an Ubuntu Live-CD for this, but you can use any that have a disk partition editor. Again make sure that it is not mounted. I haven't ever resized a NTFS partition, under Linux, you will have to look else-ware for information about that.
If you have enough room on your Linux partition, you can start from here.
Now you have to mount both partitions, you can usually do this without having to reboot your computer. Your going to have to make a decision as to where on you Linux disk you're going to place the files from your Windows partition, It doesn't have to be it's permanent location, just somewhere to hold it while deleting your windows partition.
Now unmount your windows partition, and delete it, I would just use GParted for this. If you booted from the Linux partition you're going to have to boot into a Live-CD. Resize your Linux partition, and you're done.
If you want, you can now start moving the files to where you want/need them to be located.