Question about Acer Veriton N281G

Upgrading the CPU is not likely to be cost effective, but will most likely be your biggest upgrade option. SSD is definitely the cheapest/easiest upgrade that will have immediate visible impact on performance. Really though, those micro-towers are just wimpy typically (probably running an Intel Pentium Dual Core from a few gens ago, or an older AMD dual core, neither will be very powerful due to heat constraints for the case design).