In OpenSolaris, switching to the /dev development branch is a bit like switching to the testing branch for some linux distros. So you might want to think twice before doing so, as it might sometimes break things.
If you still want to do that, follow those instructions :
Change the default packages publisher
stephane@backup3:~$ pfexec pkg set-publisher -O http://pkg.opensolaris.org/dev opensolaris.org
stephane@backup3:~$ pfexec pkg install SUNWipkg DOWNLOAD PKGS FILES XFER (MB) Completed 3/3 113/113 0.49/0.49 PHASE ACTIONS Removal Phase 28/28 Install Phase 12/12 Update Phase 227/227
Finally, perform the update of the packages to the /dev branch
stephane@backup3:~$ pfexec pkg image-update DOWNLOAD PKGS FILES XFER (MB) FSWxorg-fonts-core 2/666 872/44604 8.20/723.02 [...]
This might take a while !