For the SLB, I think it's the Edit RDB button in Media Toolbox, followed by Install AmigaOne Booter. But if you already have OS4 installed, your SLB is probably newer than that UBoot update.
If you haven't installed OS4 yet, ignore the SLB stuff for now and get UBoot updated. 1.1.1 from March 2005 is the most recent.