hmmm I think the initial docs will be centered on SM7 or the existing SC docs.
I think that the move from OVSD x.x to SM7 may need vendor support due to the complexity of it as its not a straight forward upgrade or migration - you have to maunaly move the workflows, rules and forms etc.
Moving from 5.x to SC 6.2 check the life span of SC 6.2 as this is being obseleted by SM7 so by the time you move you may need to move to SM7 - however Sc 6.2 has been around for longer that SM 7 and I would suspect that it is more stable than SM7.
There is no migration from SD 5.X to SC 6.x. The migration paths are from SD 4.5 to SM 7, SD 5.x to SM 7.1, SC 6.x to SM 7. SD = Service Desk, SC = ServiceCenter. SM = ServiceManager which will replace SD and SC. I don't think there is anything from HP on how to migrate yet. Have to wait for the official tools and guide.
HP are developing some migratation tools to aid with parts of the move from SD4.5 to SM7. These tools should be available now that SM7 has been released but clearly you wont be able to move directly from SD5.x to SM7, its likely you will have to wait for SM7.1 which is planned for Q3/4 of this year
Like Ruth says you will definetly need assistance from HP or from a HP partner to be able to move from your existing tool.