You can download it for free from the WinRAR website. Using it for free is a whole other matter, which involves software piracy that is against the rules to discuss here.
However, there is the free 7-Zip program which can read RAR archives. Not sure if 7-Zip is being actively maintained anymore, but it's probably your best free AND legal option regardless.
Hoarding photos on your phone?
Those picture are hogging memory and could be slowing down your phone.