They buy Sage 50 and start using it instead of Sage Instant.
If your question was more a technical one about transferring data, then as long as the version of Sage 50 is the same as or newer than the version of Sage Instant, then (IIRC) you can just install Sage 50 and it'll pick up and convert the data in Instant as necessary.
Do take a full backup first though, just in case things go South.
If you're installing the new software on a different machine, then that very same backup is how you'll transfer the data - you "restore" it into Sage 50.
However, consider whether they actually need to upgrade - or if it really has to be to Sage 50. Weigh up the alternatives, check out the company's actual needs and whether other software can fulfil them.
And if the final decision is to use something else, you won't be able to transfer the raw data from Sage Instant - you just take a cut off point and transfer balances and "live" transactions (O/S invoices, etc); in this case, Sage Instant can remain installed to access historical data.
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Vince M Hudd - Soft Rock Software
(I only came here looking for fellow apiarists...)