The 2-A5s to 1 A4 print option works very easily in Publisher but isn't easy to arrange in Word, so I'd recommend you have a go at copying your work into Publisher.
Using publisher the page setup and print options give you easy options for fitting two A5s side by side for printing.
bear in mind that simply shrinking an A4 document onto A5 size gives poor results.
First go to file > page setup ... then choose the 'paper size' option to get A5.
You'll find your design has 'jumped around' a bit.
You will need to alter the margins and slightly alter the font sizes, depending on what's on the page, to get it to sit nicely back on one sheet.
In word the best way to get the result you're after is to print 2 A5s and manually place them side by side on a photocopier or scanner.
Or get a packet of A5 printer paper from Staples!