presumably your camera has a 'view' mode in which you can look at photos stored on the memory card. this mode is bound to have an option to delete them.
on mine when you view a picture, there's a button to press which brings up a menu where one of the options is 'delete photo', but as pinus says, your best bet is to have a look in the instruction book
Either leave the card in the camera, then switch to 'view' mode. Select 'options' and there should be a 'delete' one. You can either delete all at once or scroll thru, deleting as you go.
Or connect the card/camera to your PC and do it that way, they'll just be filenames on a D: drive (usually-I think)
Your camera will allow you to delete any or all pictures. It will also probably allow you to "format" the card. Same effect. Alternatively, if you have a card reader on your PC, you can work with the card in the same way as a floppy disk and delete its contents or format it. Best read the camera instructions first.