You cannot select to be an ultrapeer all the time. But if you are online all the time and if people are able to connect to you directly, you will probably become an ultrapeer after being online for 6 - 12 hours.

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Morgens ess ich Cornflakes und abends ess ich Brot
Und wenn ich lang genug gelebt hab, dann sterb ich und bin tot

--Fischmob