It sounds like you are having problems connecting to download the Mavericks installer.
Hold down the Command-R keys and restart your computer. This puts you in the recovery drive where you can select to install Mavericks.
If you already have the Install OS X Mavericks installer, simply run to install over your current install.
While there should be no data loss, it's always recommended that you backup your data first. Use Time Machine or clone your drive using either SuperDuper. or CCC. Both are free to clone your drive.
SuperDuper! http://www.shirt-pocket.com/
CCC http://www.bombich.com/download.html