HI Alek.
First of all, I suggest you to copy macabre theme under other name and customize a copy. (don't forget to change theme's name in ow_themes/macabre/theme.xml)
To remove sidebar, try to do this:
- open ow_themes/macabre/master_pages/general.html ow_themes/macabre/master_pages/dndindex.html files and remove sidebar from markup.
- open ow_themes/macabre/theme.xml file and remove sidebarPosition attribute.