I have a mid-2007 iMac. 2.0GHz Core 2 Duo, 4GB 667MHz RAM, and some crappy ATI graphics card. I upgraded it from its original 1GB RAM a few years back when I was running snow leopard (2011 or 2012). It made it really smooth. However over the last few years, it has slowed down. I have about 30GB free on its 250GB HDD. Anything inexpensive I can do without upgrading the hardware? It has seriously become unusable, and I am not buying a new Mac any time soon.