I think you need to resize the partition /dev/hda3, to make room to contain all data. This will, most probably, require to modify (shrink, move etc) other partitions.
It is safer to keep backup, because every operation that modifies partitioning is potentially dangerous for the data (hardware failure, power failure, software bugs, even bad connectors and cables could corrupt the filesystem).
I had to do this myself on a 750GB external USB drive, almost full with 3 partitions on it. I took some days to backup and restore the data, and just a few minutes to delete 2 partitions + 1 extended, and expand the remaining first partition of the drive! I had no problem, so I needed to restore the contents of the old 2nd and 3rd partitions only. Nevertheless, even the 1st partition was safe this manner.
Merging partitions is long ago an asked feature for GParted. However, it isn't simple at all: what to do with file/folder permissions, with files or directories with identical names, what to do in case of different filesystems, etc.