Because I always forget ...
To update your Dell BIOS in Linux, download the .exe BIOS file from the Dell website. Extract the HDR file with "wine D630_A15.EXE -writehdrfile". This will extract a file D630_A15.hdr.
When you have this HDR file, run the dellBiosUpdate utility that comes with Dell's libsmbios:
dellBiosUpdate -u -f D630_A15.hdr
Afterwards, reboot your machine, and the BIOS will be updated.