Squareline is just a drop and drag tool for generating source code that can be implemented into your own project.
When you create a new project in Squareline you can simply change the resolution Squareline is working with in the setup screen. It does not look like it, but you can click the Resolution fileds and change them.
Afterwards, when you have completed your design and exported the source files, you will need to adjust the resolution within the diplay driver you have selected.