I'm not sure what it is called, but I downloaded this external program onto my pc that is for for windows that runs most 32 bit programs in 64 bit. I think it lets you use 4GB ram when running terraria rather than 2GB. I will post back the name of the program if I can find it.
Okay, I am not sure as to whether or not it is legal to add download links in terraria forums comments so I won't, but looking through my favourites bar in chrome, I have this link saved which I believe is the website I looked at when i got the program.
https://www.maketecheasier.com/increase-memory-limit-for-32-bit-applications-in-windows-64-bit-os/
Unsure if the program exists still but hope I helped.