Does not matter what route you go. Follow advice on http://wiki.maemo.org/Updating_the_tablet_firmware

Note that you can flash bootloader, kernel, and rootfs only or those AND the eMMc (your photo, music files etc). See page linked above.

Don'r reinstall all your progs and widgets at once as it becomes difficult to spot what may be misbehaving. Do it in batches and test.

Regarding "top", when the prog is running, press the letter "p" to filter the high cpu process to the top of the table.