Normally there should not be a problem, if!
As always before doing the OS upgrade it is recommended to do a back up- just in case.
There are, however, a couple situations in which you might consider a clean install.
The first is if you’ve done some funky partitioning of your Mac’s startup drive that prevents the Mavericks installer from creating the special Recovery HD partition.
The installer creates an invisible, bootable, 650MB partition—a portion of a drive the operating system treats as a separate volume.
Mavericks will also "updates" the EFI partition.
To see all your current set up (including hidden partitions) use the
diskutil list in Terminal