Your specs are pretty good honestly, while they could be better you aren't likely to hit any snags running games for the foreseeable future. If you really want an upgrade, I would suggest getting an SSD as Jwpanz mentioned as it will more than halve your boot-up time. Use it to store your Operating System and smaller programs (e.g. Music player, Video player, Web-browsers) whilst keeping Steam on your 1TB HDD. I was going to suggest a new PSU, but based on a power consumption estimation website you're only requiring in the region of 260W so an upgrade isn't essential.
You did mention that your PC was an "office pre-build" though, so I would do some research to ensure that your PSU is from a reputable brand. Otherwise the entire system could short-circuit! Depending on how much use your system had before you received it, I would also suggest running some tests to ensure that the Hard Drive, RAM etc are in good condition. I'm also guessing that your PC only has stock cooling, so that might be an in-expensive upgrade to consider buying if you want to ensure peak performance (and open the door to overclocking in the future). My last suggestion would be to consider your peripherals - Might you get a better experience from upgrading your monitor for instance? All I would say on that subject is to avoid "GAMING" mice / keyboards and to do your research