For accommodation upgrades, you can phone Thomson, but they may possibly charge an amendment fee as well as the upgrade cost. If you booked through a travel agent, talk to them: they just might be able to get any amendment fee waived.
Regarding drinks package, it depends on several factors: How much you drink, how much they're charging for the package, and how much time you'll be spending ashore. We did Destiny's canaries trip in January, and were lucky enough to get the drinks package for just £49 pp: Obviously we took it! Our tabs amounted to about £110 each, so we saved a lot. If we'd paid full price (£149 pp) we'd have lost on the deal. We're not heavy drinkers, but we didn't spend a lot of time ashore so were drinking (mostly soft drinks) during the day. One other point: Where we would normally drink, say, an orange juice or Coke, we found we were having the non-alcoholic cocktails during the day: Quite a bit pricier had we been paying drink-by-drink!
Enjoy your cruise!
Were you offered the drinks package onboard ship or as part of your booking.
We were offered the £49 pp deal as part of our booking (we booked in about August for the January cruise). We did check prices again just before Christmas, as some friends were considering booking to travel with us. At that time, the cruise price was lower by about £105 pp, but the drinks package was offered at £149, so the overall package price was pretty much the same as we had originally paid.