First, you would have to petition the IRS asking permission to change.  They will probably say yes.  They like businesses on Accrual. 

Secondly, you will have to rebuild your Sage 50 Company.  Sage is NOT a wet fish like QB.  You can't switch a button and have it change. 

Sage does not have an option to go from a Cash to Accrual based accounting system so you would need to start a new company and set up on an Accrual basis. You could export out your Customers, Vendors, Inventory Items, Jobs, etc and import them into your new company. You can also export out any journals, but you would have to change a column in your Sales Journal and Purchase journal from <cash basis> to the General Ledger account that represents the A/R and A/P account. If you have any Item ID's that have a Quote mark (") you will need to remove the " and replace it with 2 single marks ('), so it looks like a quote mark but is just 2 single marks ('').

The Help menu in Sage has important information on how to do this. Look up company rebuild or import/export.

This is not an easy task so please reach out to anyone out here for help.