As a rule of thumb, you can assume that if your computer or laptop had less then 2 GB of RAM installed, you best choose the 32-bit version, else you can best choose the 64-bit version. The 32-bit version will work an all machines (PCs), but if your machine it a 64-bit machine the 64-bit version will have better performance.
So let's say you want to download the LTS version, then you still need to choose between the 32-bit and the 64-bit version. Most people best choose the LTS version as it is less of a hassle and still features reasonably up to date software. This is not too complicated, but it is something to keep in mind.
#How to install ubuntu from usb on pc without os upgrade
This means you will have to upgrade your system about every year, but it is best to keep up with the latest version and upgrade every half year. This one has nine months of security and maintenance updates. However, if you want the latest and greatest of version, then you may want to download the latest version. This is great because it means you will not have to upgrade your system for a long time.
This version comes with three years of security and maintenance updates for all desktop software. The LTS version is the Long Term Support version. When you are at the "Download Ubuntu for the Desktop" page, you will usually see two versions that are available for download. You will need to choose the option for Desktop. Somewhere on the homepage, it should say "Downloads." Click here, and it will take you to a page with all the different download options.