How to Uninstall and Install feature in SharePoint

(1). Uninstallfeature

stsadm -o uninstallfeature
   -filename <file name>
   -name <feature folder>
   -id <feature ID>
   [-force]

(2). Installfeature

stsadm -o activatefeature
   {-filename <relative path to Feature.xml> | -name <feature folder> | -id <feature ID>}
   [-url] <URL name>
   [-force]