Default Windows Mobile Calendar erase?

I have an old HP iPAQ that I now only use for sat nav. It has all the software installed and working fine, even has a nice backup so when the battery goes flat from months of non use I can restore and be on my way.

Problem is there is still old calendar data in the phone that I want to erase, but if I can avoid doing a full hard reset and re-install of all the apps it would be nice...

Is this possible in a quick easy process that doesn't involve manually paging through each day?