trying to install maverick, tells me it can't it because my drive has Time Machine and is my back up, I keep backups on my iomega external drive, also says I can't put it on there because it has no partition, don't want to lose any files, HELP?

Hi I'm Barb and I am trying to install Maverick, tells me it can't it because my drive has Time Machine and is my backup, I keep backups on my iomega external drive, also says I can't put it on there because it has no partition, don't want to lose any files, have no idea how to create a partition - is there anyway I can get around this? do I need Time Machine on, can't I manually put backups on my external? HELP?