Assuming that you are using workbench mechanical, please take a look at:
https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v231/en/wb_msh/msh_glo_and_loc.html
Please note you can not increase a mesh size larger than global size (https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v231/en/wb_msh/ds_Sizing_Group.html). You will have to use largest required global mesh size first and then use local sizes (https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v231/en/wb_msh/ds_Meshing_Sizing.html) to refine the mesh as required.
-Aniket
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