[otrs] Can't locate object method "AllLinkedObjects" via package Kernel::System::LinkObject

Hi, I've got a problem upgrading OTRS from 2.2 to 2.3 The problem occurs when i click on "details" to see ticket's history. I know that ITSM 1.1.2 is not compatible with OTRS 2.3... but i don't know how to upgrade without losing data How can i do it ? Thank you Manuel Fernández Panzuela