if upgrade to 5.1.1 ur apps can be update to apps store as it require you to upgrade to ios6
if you not using cydia apps....better go for IOS6

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Added on January 6, 2013, 12:00 pm

closing of installous..might be cause of 3rd party installer which no need JB and can be download like premium speed...

i not so sure how to do it..
but u need to download the firmware first from 3rd party or apple if have...then use itune browse to the firmware location and update it..
after finish update..u need jailbreak again ...
but hackulos and installous no need install anymore as it has been shutting down..

Well, you could try restoring to ios 5.1.1 using Redsnow. Just need to grab the right ipsw for your phone. Since you're on ios 4, I assumed you have shsh blobs from ios 4 to ios 6 already. Correct me if I'm wrong here.