The easiest method is look to see if you can archive any of the older data to a separate folder. You may also want to delete any junk files you may have accumulated over time. Then you may want to look into getting an additional hard drive. You may want to look at some of the SD drives as they are fast compared to traditional drives. You may even want to take a look at an external drive with a large capacity to serve as a server. A lot depend on how often this shared folder is accessed, how many files and the size of the folder. I pick up a 4TB external drive a while back for about $125.