Wrong wool - bought DK not Aran

[OllyBJolly]

I particularly like using a few independent wool shops in rural areas I visit. I've just bought wool for a jumper and realised that it's DK and not Aran weight as specified in the pattern. I won't be visiting that shop again until September.

Can I modify the pattern - or even just go ahead and see how it works out?

Firstly Good for you for supporting independent yarn shops! They're closing at an alarming rate.
You could use dk for Aran but your jumper would end up too small. You could also try and work out how to amend the pattern but you need to be a good knitted and s great mathematician!
I would suggest you look for a new pattern for a dk yarn (ravelry is brilliant for patterns) and treat yourself to some Aran next time you visit the store x