The only upgrade you can purchase from Adobe would be Lightroom 6. Adobe does not sell older versions of their software. You could also upgrade to the creative cloud if that was a consideration. The only way you would be able to "upgrade" to Lightroom 5 is if you can find an upgrade version available from another reseller such as Amazon or B&H Photo, etc.
Ok so when I download new version can I delete the old version
Yes, the two versions are completely independent, and can coexist on the same computer. I would suggest that you leave your old version installed until you are comfortable using the new one.