So, could someone give me a step-by-step instructions about upgrading routeros on this thing?
Eh. CrapInstall seems to be the only way to go. Normis, 32MB chips were 0.17 USD more expensive? On a side note, how many programming hours would adding interface selector to netinstall take?
Seriously. How long are you in the business now? 12 years? I expected that you got bored with pulling such stunts 
If you use the single-package install and also use the single-package to upgrade, it should work fine by simply uploading and rebooting. If you installed single packages, you could have installed more than it can handle. Try to uninstall some un-used packages.
I uninstalled every package except system. After that, there was about 4MB of free space. System package is 6950629 bytes long. I didn’t install anything – wanted to upgrade freshly unboxed devices.
On 6.20 after netinstall with routeros-mipsbe-6.20.npk…
free-memory: 44.5MiB
total-memory: 64.0MiB
free-hdd-space: 5.3MiB
total-hdd-space: 16.0MiB
Maybe implementing some kind of ram-drive upgrade is a good workaround here?
RouterOS always upgrades through RAM. When you upload the package, it goes into RAM, doesn’t matter how much space you have. Did you try it ?
Even when uploading into files? Or only when hitting the ‘Download and Upgrade’ option? Does it auto-detect by .npk file extension and redirect to RAM? Thats interesting to know though I would have thought RAM would be flushed as part of the reboot process.
Yes to both. This was designed to allow upgrades on small NAND devices.
I did a /system upgrade download. If there’s some kind of upgrade-via-RAM magic going on already, then apparently you’ve forgot to fix /system upgrade to use it 
Any idea on this? Did you confirm that there’s problem with /system upgrade ?
Try to open the Files section and you will see that the there is a flash directory which will store the files after the reboot. But if you upload a file outside that directory it uses the RAM drive.
The system upgrade tool saves the files in the RAM drive and uses those when upgrading the RouterOS.
C’mon, dudes…
Am I speaking chinese here?
Let me talk to you in pretty pictures then:
> /system ssh 10.255.255.8 user=admin
MMM MMM KKK TTTTTTTTTTT KKK
MMMM MMMM KKK TTTTTTTTTTT KKK
MMM MMMM MMM III KKK KKK RRRRRR OOOOOO TTT III KKK KKK
MMM MM MMM III KKKKK RRR RRR OOO OOO TTT III KKKKK
MMM MMM III KKK KKK RRRRRR OOO OOO TTT III KKK KKK
MMM MMM III KKK KKK RRR RRR OOOOOO TTT III KKK KKK
MikroTik RouterOS 6.20 (c) 1999-2014 http://www.mikrotik.com/
[?] Gives the list of available commands
command [?] Gives help on the command and list of arguments
[Tab] Completes the command/word. If the input is ambiguous,
a second [Tab] gives possible options
/ Move up to base level
.. Move up one level
/command Use command at the base level
[admin@SB-ScreenLeft-2G] > /system resource print
uptime: 1w8h38m23s
version: 6.20
build-time: Oct/01/2014 10:06:12
free-memory: 44.5MiB
total-memory: 64.0MiB
cpu: MIPS 24Kc V7.4
cpu-count: 1
cpu-frequency: 400MHz
cpu-load: 0%
free-hdd-space: 5.3MiB
total-hdd-space: 16.0MiB
write-sect-since-reboot: 159
write-sect-total: 1284
bad-blocks: 0%
architecture-name: mipsbe
board-name: RBcAP2n
[admin@SB-ScreenLeft-2G] > /system upgrade
[admin@SB-ScreenLeft-2G] /system upgrade> export
# jan/09/1970 09:33:41 by RouterOS 6.20
# software id = RC64-4A6Q
#
/system upgrade upgrade-package-source
add address=10.255.255.254 user=upgrade
[admin@SB-ScreenLeft-2G] /system upgrade> refresh
[admin@SB-ScreenLeft-2G] /system upgrade> print
# SOURCE NAME VERSION STATUS COMPLETED
0 10.255.255.254 routeros-mipsbe 6.21.1 available
1 10.255.255.254 wireless-fp 6.21.1 available
[admin@SB-ScreenLeft-2G] /system upgrade> download 0
failure: not enough space on disk
[admin@SB-ScreenLeft-2G] /system upgrade> #FIX PLS KTHXBYE
[admin@SB-ScreenLeft-2G] /system upgrade>
So what did I do wrong? Maybe I should dance for a while before hitting enter?