You don't need to reinstall. 4.X installations can safely be upgraded to 5.X. Upgrading older releases (1.X, 2.X or 3.X) isn't possible. Our latest 5.2 installer can be found here: http://lansweeper.com/Download.aspx
Update instructions can be found on page 191 and beyond of our online documentation: http://www.lansweeper.com/documentation.pdf
We do recommend performing a database backup prior to upgrading, just to be safe. Right-click on the lansweeperdb database in SQL Server Management Studio and select Tasks/Back Up. If SQL Server Management Studio isn’t installed on your Lansweeper server, we recommend downloading it online. (You will need to perform a search for the Management Studio that’s compatible with your particular edition and version of SQL Server.)