When we run desktop client on local machines we often get Ouf of memory error and have to close the application and start it again.
The SQL database is MS SQL Express with 1GB memory limit.
Does anyone know how to solve this?
The problem is probably not in the SQL Server memory limit since it is the Desktop client which is out of memory.
You need to optimize the amount of data you work with, e.g. by not loading too much data in sequential workflows or to set-up lazy-loading in screens so not all data are loaded when opening a screen.
You should study the log for the exact cause, e.g. which workflow step caused it.