Start by checking if you actually need a faster broadband speed.
If
(a) you live in a house full of teenagers, all wanting to stream Youtube and iPlayer content at the same time ; or
(b) you want to download massive files (such as movies) to permanently save them on your computer (rather than to simply watch streamed video content online)
then a really fast broadband speed might be good for you. Otherwise it's simply a waste of money. (A download speed of 10Mbps is all you need if you live on your own and don't want to download really big files. You wouldn't notice any much difference if you had a download speed of 1000Mbps)
So check your current download speed here:
http://www.speedtest.net/
If you're already getting at least 10Mbps (or even just a bit below that) that's probably all the speed you need and 'upgrading' would simply be a waste of money.