You simply need to modify your document template piece. Every time you make File > New, Solidworks loads your part model, which in your case is set to CGS.
So you need to edit it, File>New> you change your units, and you save your part template, File >save as> you change the file type to: part templates *.prtdot, and you overwrite your initial template. That way you won't have this problem in the future.
If it is in your drawings , you have to adjust your settings in the document options (drawing) and then save the document as a template (. DRWDOT) with the basemap (. SLDDRT).