The current theory on upgrading from an older version like 5.0 is to upgrade to v5.1.2 or v5.5 first then to 5.6 then to 6.0 (or 6.0.10).
There were significant changes between those versions, particularly 5.5 to 5.6, so incremental upgrading will give you the least problems.
You should uninstal all add on contrib rpms as many of those designed for v5.0 will be incompatible with 5.6.
You should really be running v6.x now for security reasons. Earlier versions are no longer supported.
Also be aware if your box is a few years old (ie circa v5.0),the hardware may not be good enough to run v5.6 or v6.x on it, depending what you want to do with it of course.
Regs
Ray