Error in purchase category - Help Please

I was looking for some way to put some dappled light into a recent photograph.
I searched for ways to do this and found the wonderful FilterForge.
I followed it on Youtube and this made me extremely keen,
When I went to the Filterforge web site I downloaded the trial version - fantastic.
I then found that if I purchased that day I would save 200% of full purchase price. I couldn't risk losing that offer and so immediately purchased the standard version (49$)
It all looked so good until I tried to open one of my own images. As I tried to open my image file I was warned that I could not use a file of over 3000 x 3000 pixels in the Standard version of Filterforge. My camera produces files far larger than that.

I have now seen that if I had purchased the professional version for 79$ I could use files from my camera.
I am hoping pay the difference to take my Standard version to Professional but cannot find a way to do this. I do realise that I am responsible for my purchase error, but did not take advantage of the 30day trial for fear of losing the huge discount.

Advice, help please