Is your upstairs TV set already 'smart'? i.e. can it connect to the internet (via your router), so that you can watch catch-up TV services (such as BBC iPlayer, ITV Hub, All 4, My5,etc), as well as things like YouTube, on it? If not, an Amazon Fire Tv Stick will turn your 'non-smart' TV into a 'smart' one. The types of services I've just mentioned are all freebies.
However if your TV set is already 'smart', an Amazon Fire TV Stick won't add much functionality to it unless you use the paid services that it allows you to access. (NB: Some 'smart' TVs allow you to access some such services anyway, without the need for a Fire Stick, so you need to consider whether or not you'll be getting much extra through purchasing a Fire Stick).
Probably the main service that people buy Fire Sticks for though is to enable them to access the services which are available to Amazon Prime members. Amazon Prime costs £7.99 per month and, as well as getting you free delivery on items purchased from Amazon, also enables you to watch hundreds of thousands of movies and TV episodes:
https://tinyurl.com/y6cw577k
There are other subscription services available through a Fire Stick though, including Netflix. (NB: As I've indicated above, if your TV is 'smart' it might already be able to access Netflix, so a Fire Stick wouldn't add anything extra in that respect). Netflix costs £8.99 per month for their HD service or just £5.99 per month to watch in SD. (Quote: "Netflix has an extensive library of feature films, documentaries, TV programmes, anime, award-winning Netflix originals, and more").
https://www.netflix.com/gb/
There are alternatives to the Amazon Fire TV Stick available. They include Roku devices, which do much the same job as Fire Sticks do and cost around the same price. (The Roku Express is currently on offer for just £17.99 though:
https://www.roku.com/en-gb/products/roku-express#where-to-buy ). There are also devices from Now TV, which can be useful if you've not got satellite TV, as they provide access to a subset of Sky channels. (For example, an 'Entertainment Pass' costs £9.99 per month and provides access to all Sky's non-movie entertainments channels, as well as to National Geographic, the Discovery Channel, etc. A 'Cinema Pass' costs £11.99 per month and gets you over 1000 movies to stream on demand):
https://www.nowtv.com/