Gigaset GS290
e-2.5-s → e-2.6.3-s
update through recovery on SD-card, basic applications are OK.
but new behavior for next udate, see :
or:
new; the GS290 is now at version e-2.6.3-s, after updates via recovery with SD card. Looking at:
settings → applications → all → “…” → process-system → update manager → mobile data and wifi
I see that I can enable: allow-network-access, data-wifi, mobile-data (were they grayed out before?).
Then, the Update-manager tells me (today) “no new update available” as expected. I can’t wait to upgrade to e-2.7 
thank you very much to those who helped me explore the dense tree of parameters, and use the “recovery” mode.