How do I get sar to show for the previous day?

Usually, sysstat, which provides a sar command, keeps logs in /var/log/sysstat/ or /var/log/sa/ with filenames such as /var/log/sysstat/sadd where dd is a numeric value for the day of the month (starting at 01). By default, the file from the current day is used; however, you can change the file that is used with the -f command line switch. Thus for the 3rd of the month you would do something like:

sar -f /var/log/sysstat/sa03

If you want to restrict the time range, you can use the -s and -e parameters. If you want to routinely get yesterday's file and can never remember the date and have GNU date you could try

sar -f /var/log/sysstat/sa$(date +%d -d yesterday)

I highly recommend reading the manual page for sar.

Try the command as follows to get historic memory utilization details.

sar -r -f /var/log/sa/sa01

The files in /var/log/sa record everything in the world.