Hello,
Having done exactly that 50 million trillion times, as most of us have
IF you have not made changes to your Tables and Fields in any way then simply installing your shiny new Component in Joomla! will perform an update, and all should go well.
IF you have made significant changes to the Database then you best Uninstall the existing Component and then install your new Component.
That being said, even though you will loose your data, in early stage install testing I always Uninstall (for that clean fresh taste!) and then Install.
If you need to keep your data safe and sound please use phpmyadmin or similar and perform an SQL Dump of your database with the data.
Hope that helps,
Regards,
Edward.