How to change a library refence in modelsim?

Are you trying to do a post synthesis simulation or RTL simulation? If you're doing a RTL simulation you need to include the altera_mf and any other altera library in the VHDL code.

library altera_mf;

Use altera_mf.all;

You could try using the above statements in the VHDL code. Open the altera_mf library source code and see under which component is the module in question. include that in the "USE altera_mf.<component_name>.all;

If this doesn't work, then what you can try is to compile the altera_mf VHDL sources/library into your work library. This will include all of the required modules and your design will compile & simulate.

If you're doing a post-synthesis simulation the libraries will get used by default.