Updating a specialised allez

[veitch1]

Some advice needed if anyone can help. I have an Allez (2005ish) which runs tiagra 8spd cassette (12-25) and derailleur and a 39/52 chainset. I have sora flightdeck changers. All the above have had a bit of use and also it's quite hilly where I ride.

Was thinking of getting a 11-28 10spd shimano 105 5700 and same derailleur but does this mean I'll need a new changer as well? Even secondhand that puts the price to far more than I paid for the bike!

Thanks to all that reply!