Type this into shell via SSH/serial/telnet (kolofonium is what is needed for a raw fonera)
The meraki mini apparently runs at 115200 baud over serial, the fonera uses 9600 baud

16 MB models

mirrors from this site:
http://fon.testbox.dk/flashing/redboot_16MB_RAMdevices/openwrt-ar531x-2.4-vmlinux-CAMICIA.lzma
http://fon.testbox.dk/flashing/redboot_16MB_RAMdevices/out.hex

external site/general instructions:
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cd /tmp
wget http://fonera.info/camicia/openwrt-ar531x-2.4-vmlinux-CAMICIA.lzma
mtd -e vmlinux.bin.l7 write openwrt-ar531x-2.4-vmlinux-CAMICIA.lzma vmlinux.bin.l7
reboot
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  (wait and log back-in)
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cd /tmp
wget http://fonera.info/camicia/out.hex
mtd -e "RedBoot config" write out.hex "RedBoot config"
reboot
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upgrading to 32MB
Meraki Mini is included here (also if you modded your fonera with additional ram)
However, the Meraki mini ALREADY COMES WITH REDBOOT INSTALLED! YOU DON'T NEED THIS GUIDE IF YOU HAVE ONE.

First install redboot via the 16MB method.  You'll need to download the redboot32mb.rom file from the '...flashing/redboot_32MB_RAM_devices/' folder on this site.
Host that file via tftp with tftpd32 (othertools folder) or pumpkin (set your wired ethernet card to IP 192.168.1.166 and connect it to WAN/LAN on the fonera). 
Then get to the Redboot prompt with serial or port 9000 over telnet and type this in:
_______________________________________
load -r -b %{FREEMEMLO} redboot32mb.rom
fis create RedBoot
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If you have the tools to solder ram...
http://www.dd-wrt.com/wiki/index.php/LaFonera_Hardware_32MB_SDRAM_MOD
Credit to Goldserve