Your processor is the Atom N455 according to page 27 of
http://download.lenovo.com/UserFiles/UserGuide/en/User%27s%20guides%20and%20manuals/S10-3c/Lenovo%20IdeaPad%20S10-3c%20Hardware%20Maintenance%20Manual.pdf
It is a 64 bit processor: http://ark.intel.com/products/49491
You want the latest version 6 of Trisquel for 64-bit processor:
https://trisquel.info/download
Either the "normal" GNOME version or "Trisquel Mini", a lightweight version
of Trisquel (with the LXDE desktop rather than the GNOME one). Your hardware
can handle the normal version. However, it may face troubles (become slow
because of swapping) if you open many heavy Web pages in parallel while using
other heavy applications such as LibreOffice.
Buying one more GB of RAM may be a good and rather cheap (about US$ 10) idea.
According to the specification the manual for your laptop, you want 1 GB of
DD3 RAM at 1333 MHz. You cannot have more (2 GB is a maximum for your
motherboard).
