Do you know how to email a picture to anyone (rather than just 'to your computer')? If so, simply email a copy to your own address and then access your email via your computer.
Otherwise you might be able to connect your phone to your computer via suitable lead (possibly the same one that's used to charge your phone) or you might be able to remove the memory card from your phone (if it's got one) and insert it into a card reader. It will be a lot easier for us to provide precise instructions though if you'll tell us the model of Doro phone you've got (so that we can then find the manual for it).