I deleted the themes … but they still show up and work ??

Hi,,I have been trying to make some changes to the coding.

To make it easier I thought that I would delete all the themes that I uploaded so that I only use the one theme that I have decided upon.

So I deleted the other themes from my server.

When I go into WordPress – I find that all the themes are still showing as optins and the that I can use them all – EVEN though I deleted them from my server.

How on earth can this happen ?
Any ideas – it will also expain why my code changes are not showing up !!

Thanks