The card reader in my experience tends to come up as another drive. If you go into "my computer", can you see it there? If so, you can browse and delete the pictures as if they were already on the PC. Or just copy over the ones you want.
thanks MaryBS I can do that its just a pain when it takes so long to download photos as its downloadings ones I already have saved
I went into Tesco to print some photos off my memory stick and had to give up as it was taking so long to download all the photos even though the camera was telling me there were only 30 on it, the machine was showing >200 so they have to be on the stick itself somewhere
As Mary sugguests plug in the card / card reader and when it tries to download the pictures select cancel. Then open Windows Explorer and look for a new hard disk. On a simple PC setup it will probably be the "E" drive.
Browse into that drive and you will probably find some folders named with 4 letters, eg DCIM. Look in those and you will find lots of .jpg files (for most cameras). Delete any of these with a timestamp older than before you reckon you took your new photos.
Once that is done unplug the card reader and start again and see if it has a shortened list of photos to download.
Once you have the photos you want put the card back into the camera and using the system menus find a "Memory Card Format" option and use it to clean your card completely.
I am guessing you have recycled a memory card from another camera without formatting it first.
If that doesn't seem to work, go the long route of downloading all the photos from the card onto your PC, but Tick the little box that say "Delete Photos from My Device once downloaded" (I paraphrase).