It's really simple. My recommendation:
1. Buy 4 GB SD card
2. Create folder Garmin in a Fat32 formatted SD.
3. DL City Navigaror Europe NT 2014.40 from here: Garmin City Navigator Europe NT 2014.40 Unlocked (download torrent) - TPB
4. Copy unlocked map (gmpapsupp.img) in to Garmin folder on your SD.
5. You are good to go!
- other files from torrent are not relevant because your device doesn't support them (gmap3d.img).
- delete your old map from your device. It's located inside Garmin folder named "gmapprom.img"
- connect your device with your pc, install garmin webupdater and check for software updates for your nuvi.
- You might come across with the latest map - Garmin City Navigator Europe NT(Unicode) 2015.10 but it's in unicode standard therefore is NOT good for older models like Nuvi 265! That's why I recommended the latest NT version.
- If you live across the Atlantic, than you need NA map: Garmin City Navigator North America NT 2015.10 Unlocked (download torrent) - TPB