I have to unmount my sdcard when I download some apps to do that hit menu>storage & sdcard> and under utilities select unmount SD card. After that try to download your maps.
To delete those PDF files you can use your computer by plugging in your DI and select disk drive. Open your sdcard and locate the file downloads which the PDF's should be in then just right click and select delete.
To delete them using a file manager like astro on your DI open the program and select SD cards>downloads then find the files and either press the file and select delete or long press the file and select delete depending on which file manager your using.