Header logo shrinked

Hei!

This is another problem that I face, maybe it relates to the new evolve update. The header logo (cover) for our webpage shrinked considerably and now it is almost impossible to see clearly. I tried uploading it again, but when I try to upload it set it as header the save the draft and preview it, it is 1) out of proportions 2) shows the old, small logo in front of the newly uploaded one.

I guess the most ideal would be if the header size reverted to normal, but how can that be achieved?

Thanks in advance!