[xwiki-users] Some problem about Upgrade from Xwiki-5.4.5 to 7.3

I want to upgrade from Xwiki-5.4.5 to 7.3, but some problems occurs. I create a backup db, and run 7.3 instance on the backup one. 1. The "Spaces" feature seems disappears, all old spaces are organized in a single root tree. I can not manage access privilege by Space. 2. The wikis application can not be removed, there is nothing in the "Installed Application", and I DO NOT want the multi wikis. 3. I want to export the old content from the old wiki, and import it into new wiki, but I cannot export only my selected Spaces. Anyone can point me some way to solve?