marking an upaid invoice as paid (at a later date on ledger 1.3.23)

Hello, first time poster so please bear with me a little.....

all a little background info for you all. I have been using ledgersmb 1.2 series for a few years with no problems at all, (i took over a company that was already using ledgersmb) and continued to use this happily making regular backups etc, with that being said, aproximately 6 months ago now we suffered major problems due to a harddrive crash on the pc that ran the whole database/ledgersmb as a whole.
To cut a long story short we eventually managed to transfer the database onto the latest approved version of ledgersmb at the time (1.3.23) with alot of help from some very helpfull people through this site.

However one big problem that i am still trying to work out is how to mark unpaid invoices as paid at a later date on the new 1.3.23 version. before on verions 1.2 etc it was simply the case of clicking - Cash - Recietes and once on the recietes page with relievent customer sellected it was as simple as clicking the box to the right of each unpaid invoice, updating method of payment at the bottom along with date paid and post, JOB DONE. now the new 1.3.23 still uses the exact same tabs down on the let hand side of screen and still shows - Cash - Receite, but after actually getting to the Reciete page i am completely baffled as to what to do next, can anyone please explain the workflow required to mark invoice/invoices paid later on once at the Reciete page as i have spent many an hour trying to work this out with no such luck, either thator Im actually going mad!

I have already checked in the user manual which although mentions the cash - recietes part but fails to go and explain in what order i need to do whatever it is that i need to do to achieve said outcome?

Again appoligises if this makes little to no sense or if I havent used the correct terms but Any help / abuse would be much appreciated, Thanks in advance Don @ Beamends