Is there a way we can Delete files from destination before Copying new files to the destination ?
The option "Delete files from destination that don't exist in the source" occurs after newer files have been copied to the destination, this however at times is difficult when space is tight and it would be useful if the unwanted files could be deleted first to make room for the new ones.
I don't think there is a way to re-order things. (I thought it already did it in the order you want, but I'm probably confusing it with something else! Maybe that only happens with the clashing files, not the ones missing from the source.)
If you are only dealing with a flat directory (i.e. no sub-folders) then there are other ways of doing it. Shout if that is of interest. (Probably not, though, given your previous question about sync limits. )
It appears obvious that while the synchronization task is performed, i.e. newer files that exist in the source are copied and overwrites older files that exist in the destination, and after that in the task window it then deletes, i.e. "Delete files from destination that don't exist in the source"
I cannot see any options that would change this synchronization order, "Delete 1st, then copy".
If there is not such an option, perhaps we should request a synchronization for, to only "Delete files from destination that don't exist in the source"