According to this page at Epson, the BX 305
cannot scan slides:
http://www.epson.co.uk/Store/Printer...articleId=1045
This means you have three choices:
1) buy a new flatbed scanner that can scan slides
2) buy a dedicated slide scanner
3) use a scanning service
Which route is best for you will depend on your budget, where 'budget' isn't just the size of your wallet but also takes account of the fact that getting a good scan of a slide can be time consuming.
None of the options are 'cheap'. Well, you can get cheap scanner but I guess you took slides in the first place because of the quality they offered so it's unlikely you'd be satisfied by the output from a cheap scanner.
Ken