Help Needed - Blank Sheet Formatting has altered!

I hope someone can help. I have been using Excel for years at work and at home. I recently downloaded a template to help with my family history research, and somehow it has changed all my  blank workbooks to that format. which has a huge frozen block at the top of the page with the useable portion fitted into a couple of lines at the bottom. I cannot work out how to correct it....  I am sure it is something so obvious that I am missing....