1. I fail to see why you are mentioning a Macbook in your question if it's about upgrading a Dell.
2. All you can upgrade in a laptop is (1) add RAM, (2) replace HDD by a larger one or by an SSD.
So it seems after 6 years you want a new laptop. Quite a long lifespan for a laptop.
I had purchased Dell Studio 1558 (I-5 1st generation, 15.5 " http://www.dell.com/support/home/us/en/19/product-support/servicetag/3cnx4bs/configuration) in year 2011 and Dell didnt deliver what they promised as after two year it started throwing blue screen. Display is working fine.I need advise if I should buy Macbook which will be 4 times expansion then upgrade. I want to use SSD hard disk, 32 GB ram. I need expert advise on it so that I can use my existing Laptop outer cover and place Motherboard in it with latest RAM+ Processor.