how can I remove pictures from SD card with out down loading pictures first

Use Image Capture instead of iPhoto to erase the card.

Launch Image Capture, select the card in the sidebar.

To remove items from the device after transferring them to your computer, select Delete after Import in the lower-left corner of the window.

Reformat the card with your camera.

Yes, reformatting is perfect for erasing all at once, but for deleting selected photos without importing I only know Image Capture. It is very convenient to be able to simply select photo on the card in the Import window and to click the delete () images button..

I read that as all or nothing, but you're right. On re-reading it does suggest that the OP wants to selectively delete images.