Old thread but always handy if people are looking for this answer:
go to your calibre folder located @
C:\Users\%username%\AppData\Roaming\calibre
open gui.py.json and search for"save_to_disk_template_history": [
you should find something like this: just delete the templates that you no longer need and restart calibre
"save_to_disk_template_history": [
"{author_sort}/{title} - {authors}",
"{author}/{title} - {Authors}",
"{author}/{Series}/[{series_index:0>2s}-{Series}] - {title} - {Authors}",
"{author}/{Series}/{series_index:0>2s}-{Series} - {title} - {Authors}",
"{Author}/{Authors} - {title}",
"{Authors}/{Authors} - {title} - [{Series} {series_index:0>2s}]",
"{#mytag}/{Series}/{authors} - {title} - [{Series} {series_index:0>2s}]",
"{Authors}/{Authors} - [{Series} {series_index:0>2s}] - {title}",
"{author}",
"{#mytag}/{Series}/{authors} - [{Series} {series_index:0>2s}] - {title}"
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