Look in System Maintenance -> System Status
There are two firmware versions listed.
Firmware Version and ADSL Firmware Version
The first one, "Firmware Version" gives the router firmware version.
The second one, "ADSL Firmware Version" gives the firmware version that's driving the ADSL chip.
The different ADSL firmware versions are sometimes for different countries or for different line types. Generally the latest release of adsl firmware version has the higher number. New adsl firmware versions might have improvements for interoperability with DSLAMs or newer protocols (such as ADSL2+ Annex M)
There isn't generally much information available regarding any specific modem version.
The file name of the zip or .all / .rst file can often tell you what firmwawre version it includes. For example v2820_3321_232201_A.zip has firmware vesrion 232201
As a general guide use what's recommended for UK use based on the download on the DrayTek UK web site but if you find specific issues on your line it's sometimes wortwhile to try the other firmware versions from draytek.com (provided they're listed as Annex A and not Annex B) to see if that's better for your situation.
