Basically what jefe posted is a guide to the best version of overclocking which is done through the BIOS.
You are asking about software though and based also on your system name (Acer Aspire) you have a notebook which is typically not suggested for overclocking as they do not have sufficient air flow or heat dissipation.
For most OEM computers, even their high end expensive ones, they lock the BIO since they use a very generic one done by one of the major mobo makers (normally Asus or the like) or if you are unlucky, a unknown mobo maker. This means that the mobos are cheaper in production. So unlike major mobo vendors like Asus, Gigabyte and so on who use 100% Japanese Solid State capacitors and high quality phase voltage regulators designed for overclocking, these are cheap caps that tend to blow easily and have bad voltage regulation.
Add to that the fact that they use low end power supplies that only supply the needed voltage to the components and overclocking becomes further futile.
In short, you are best to not overclock. It would probably end up in the death of your laptop.