Decompress cactistoric.tar.gz in your Cacti directory.
cd CACTI_DIR tar xvzf PATH_TO_cactistoric.tar.gzCustomize the number of row a rra should keep. I use 17280 rows in daily RRA to have 2 month of 5 minutes average data. In Cacti go to -> -> and modify the Row value of Daily (5 Minute Average).
Resize the already created RRAs with the command rrdtool resize. See RRDtool documentation http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/manual/rrdresize.html for more information. If you previously created rra with the Cacti default value (600), use the following command to resize them at 17280.
for f in `find . -name \*\.rrd` do rrdtool resize $f GROW 166800 done