If you have MASM installed and wish to use that instead, it may be done manually.
First, set a path to where the MASM files are located (Options-> Set Paths -> User Path
Next to change the default behavior of HIDE for all future files, you need to edit the HIDE\bin\khla.ini file. To change the behavior of just one project, you need to edit the .hpr file.
Find [KHLA Settings].
In that section, there is a key label "Assembler=fasm".
Edit it to read "Assembler=masm"
From that point HIDE (and KHLA) will use MASM to assemble the output.
Note: If going with MASM, you may also decide to change the options for the librarian, linker and resource compiler to their
respective names in the MASM32 package.