I assume that your remote is like the left hand one in this photo, with an AV button in the middle of the second row of buttons. If so, we tend to call it the ‘AV version’ and this will not allow PC to be added to the LIST button. You cannot update the software, but theoretically you could replace the motherboard and buttons to change it into a newer version that allows you to add the PC version to LIST. This is unlikely to be cost effective, hence I would simply look for a newer remote (any of the others pictured) or find an older Beolink1000 (BL1000) which will allow you to access PC by pressing SHIFT then STORE.
On UK eBay, newer Beo4s sell for between £30 and £50 and BL1000s approx £30. Often you have to be a bit patient as sellers can ask for more.
EDIT: There are Hotel versions of Beo4 with reduced functionality – they usually have less marked buttons that any of the ones pictured, and probably would not have the PC functionality.