Buy a scanner. Loads to choose from at PC World, Jessops or similar. I'm not even going to begin getting into the debat of which is best
Quality of scanned images will depend greatly on
both the quality of the scanner
and the quality and size of the original print.
If you get a scanner with a sufficiently high resolution, you
may be better off trying to scan the original negative. You can get software which handles inverting the colours.
Get yourself
plenty disk space and look forward to hours of swapping prints into and out of your scanner
HTH