how to delete quartus2 has been bulit project files?

For your question, if you mean how to clean up the Quartus Project. You will have to manually delete files. The generated output files are the ones named .sof . If you on the other side perhaps just want to generate a new Quartus-File then try File/New. You then have to select the fileformat you want to use for the design. If you want to add a existing file go to the file-tab on your screenshot right click and add the file you have prepared.

(I recommend not to use blanks in Quartus-Project paths. What language do you speak normally? Try to rephrase your question with more details.)