See if your Systems Administrator has installed sar and the associated data collection and reporting crons (man sadc). The default daily report includes memory usage and a lot more, but it would be better to make your own custom report which contains just what you need (for example sar -f /usr/adm/sa/sa?? where ?? is the day of the month). Not sure if you would need root access to run your own reports.

The main issue with historical reporting as distinct from dynamic monitoring is that you must have an automated background process to save the data. If not, your whole life will get taken up with running monitor processes.

Wherever possible I prefer to automate any management reporting and then email the report direct from the server. The management like to read short summary reports which clearly state that the system has no problems, or clearly state that the system needs upgrade or replacement.
If you need a fine-detail report for you own purposes, then send it to yourself or your team.

Sometimes you have to plot graphs in Excel and this means taking some serious time to develop scripts which produce data files which require the absolute minimum of effort to plot the data in Excel. To this end I use ftp to deposit the data on a Microsoft Server and have a ready-prepared Excel spreadsheet to plot the graph.