If you have installed the correct USB drivers then when you connect your phone to your PC, you will see a USB connected Icon on the phone. To See the SD card from your PC, you need to Mount the SD card from the phone.
Menu
Notifications
USB Connected
Mount.
You will now see the SD card and all it's contents as an extrenal drive on the PC. Copy and delete to your hearts content.
If you wish to manage your contacts I'd suggest doing it via your google account, as it's much easier. Just re-sync back to your phone when your finished.
There is in fact 3 forums here all about the same phone.
See Also
Samsung Galaxy Portal forums
and
Samsung Galaxy Spica forums
The GT-i5700 goes by these names depending on where you live.
As regards to why there's Galaxy Lite, Galaxy Spica and Galaxy Portal forums, when in fact they ARE EXACTLY they are all the same phone is probably an error when they forums were set up. It has already been asked to merge these, but word is it's too difficult or too hard, or time consumming to do.