I am not sure what you mean, but I will try to elaborate.
If you for example have Sitefinity 3.5, I will advise you to upgrade to 3.6SP2 without going through all service packs between the two editions. Sometimes there is an upgrade path you should follow, since the changes are too dramatic, but we do not have such case Since Sitefinity 3.1. It is even possible to upgrade from Sitefinity 3.2 to 3.6SP2 directly.
Just let me know about the exact case, and I will let you know about the process.
the Telerik team