Main menu - Tools - Options - General
Working directory - this is the folder where all files for new tasks will be saved by default.
Minimal disk space - AbleGet will stop when free space on the disk (where files are saved) become lower than this value. It's recommended to leave at least 30 MB for system (usually c:) drive.
Delete to recycle bin - all files deleted by AbleGet may be send to Recycled Bin.
Click here for description of other options.