Best solution: increase the amount of RAM. Most easier way is to double it if you have free slot(s), or replace the DRAM modules with new ones with larger size (look at motherboard manual or manufacturer's support for RAM compatibility list).
Less good solution: free some OS memory by removing some resident programs, uninstalling unused drivers and services. Two utilities may help in this: Process Explorer and CCleaner. Before any change, consider to create a restore point.
a) Remove the residents: look at the Startup list in CCleaner and also in Process Explorer and disable the components which are not vital for OS and your work, like autostart of messengers, additional sound drivers, different check-for-update programs, manufacturer's services etc.
b) Uninstall the drivers for external devices which you don't use or use very infrequently. Also uninstall the components which you most probably never use, like 3D Vision driver from NVidia.
c) Look at the list of services using the Process Explorer and decide which services can be changed from automatic start to manual and which ones can be disabled completely. Do this in Computer Management, Services. Change the settings with caution and always check the OS functionality after few changes!