Hello I am interested in updating my license, the firt time I got my license was on october 21/2016, now the version I am using is 4.8.3. I would like to know which one I should download and how much is the cost of it?. I am using MAC OS 10.13.6 could I upgrade to LRT5 ?....

You'll always find the latest Download on https://lrtimelapse.com/download/
MacOS 10.13 will work, but you'd need to install an additional library, as mentioned in the install notes: https://lrtimelapse.com/install/
You need to upgrade your license, there is a discounted upgrade on https://lrtimelapse.com/upgrade/