I had a feeling that was the case, thanks for taking the time to reply, I appreciate it.
What would you suggest? Is upgrading to a better processor a difficult task? I have minimal knowledge of computer hardware etc.
Anyone that says your hardware isn't enough for this game is full of it. Except for the highest end games, you won't really see any benefit to upgrading to a quad core cpu or higher. In saying that though, if you have the funds, you should certainly think about upgrading in the near future as many programs today are starting to take advantage of having more cores.
It is actually a very simple process to install a new one, but there are a few things you should know first. Your i3 550 is an older model cpu which uses the 1156 socket motherboard, so parts will be alittle difficult to find and will usually be more expensive than current ones. For instance, an i5 760, which would work in your motherboard costs around $250, but a current i5 3570k costs $220 and is much faster, but it uses socket 1155 motherboards so you would have to buy a new one.
Watch the video on this link to see how easy it is:
If you are looking to just increase performance for gaming in general, you might also want to consider buying a better graphics card.
Upgrading will certainly help your situation, but it won't make it perfect. Here's my pc specs and I still get weird fps drops.
i7 2600k OC'd to 4.5Ghz