Hope you have done Database back up and the web.config file

step 1: login as Admin


step 2  : http://mysite1/sitecore/admin/updateinstallationwizard.aspx


step 3: downloading packaging 

  1. upgrading sitecore to till sitecore 7.5 download package from https://sdn.sitecore.net
  2. upgrading to sitecore 8 and above download package from https://dev.sitecore.net/Downloads.aspx
  3. if you wants to know features sitecore versions || features