It would likely be very helpful to upgrade your RAM, almost any computer from 2013-2015 can easily be upgraded to 8 GB of RAM.

I have to wonder why you use Sage 300 with only one user? 

How are you doing your backups?

I am a little surprised that you are able to run Sage 300 CRE version 18.4.1 with the existing system configuration.

Please refer to this link for the recommended system requirements.   https://support.na.sage.com/selfservice/viewdocument.do?noCount=true&externalId=104860&sliceId=2&cmd=&ViewedDocsListHelper=com.kanisa.apps.common.BaseViewedDocsListHelperImpl 

You can also find the system requrements in Sage Desktop, Help, Product Documents, select Sage 300 CRE, then the version, then the System requirements article.

Thank you...  I appreciate the help!

We used to be a much larger company with multiple client machines, now we are tiny but chose to keep Sage 300 CRE because it has worked well for us for so many years.  When I started with the company in 1998, we used Medallion and we have stuck with them since.  I backup the entire directory onto an external drive.

I recommend that you upgrade the RAM on the computer as Brian suggested to at least 8 GB prior to insalling 20.3.