You shouldn’t be trying to do anything online whilst doing a speedtest, it will skew the results wildly. Plus your upload for the wedding album could only be 25% or so of your download speed.
Your router could be knackered if its overheating, it shouldn’t overheat however hard its working. You could replace this with a generic one from PC World etc. If its wireless, this can cause performance issues itself, try plugging in with an ethernet cable instead, and disabling the wireless temporarily.
Otherwise, if your broadband is slow all the time even during off peak periods, its due to a low quality line or the distance from you to the exchange, and there’s not much you can do about it unless you believe its faulty (crackling on the line etc). If its slow during the evening when its busy, it might be worth doing a Google and seeing how Orange compares to other ISPs, specifically you are looking for the contention ratio. This is how many users share a specific amount of broadwidth as allocated by Orange. If its a high contention ratio (quite likely if its their basic service) your service will get slower as more people go online. Business orientated services usually have the lowest (and best performing) contention ratios.
P.S your wedding album, if you are uploading full size pictures it will take ages, you can resize them to say 800×600 and the file size will reduce to a fraction of the original.