Is there a way to extend or reduce the width of a glyph by a certain percentage?
Instead of selecting the entire glyph path and dragging the mouse, I want to change it by inputting numbers. In particular, I want to change several glyphs at once.
You can use the Transformation panel, with theses settings :

Oh…! Thank you!!
There was unlock button! I didn’t know because I’m not familiar with Glyphs yet.