I have been using knime to do some learning on images and when I load in a large data set of images there isn't enough ram on my machine to handle it so it starts to write to disk as usual but the disk that it is writing to is almost full and I would like to know how to change the disk that knime decides to write to
you can change this in the preferences.
Therefore goto File -> Preferences -> KNIME and change the location of the temp folder.
I'm sorry to hear that. Another option might be to process the images on an image-by-image basis, e.g. by using the Streaming Executor or Loops. You can find some examples here:
https://www.knime.org/nodeguide (Community Category).