Its is not recommended to upgrade like that. Pls see if you can find space. Also if you already have a latest backup taken you can skip the creation of backup step during upgrade.If you want to move around your perfdata file to a different path like NFS mount point( only perf dir and not the data dir) use the dfm datastore setup cli to move the files.
Pls upgrade to 5.0.2 P1 release instead of 5.0.2 as this has additional fixes. The perf flat files which are of size 2 to 4 GB would automatically be cleaned for stale instance post upgrade to 5.0.2. The reason for the big flat files can be found in this bugs online link.