What you are referring to is a lentil beam of some sort to carry the load of the wall and home above.

If there is a window their currently and you do not enlarge the width, you will use what is existing and not have to change the lentil.

In most egress retrofits, if you are tearing out a basement 2-Lite slider or hopper, you can easily put a casement of the same width in that opening and elongate the window opening downward to get the proper total square footage.

Most applications require that you need to move the hole down to get the ledge of the window within 44" from the floor.

Due to the cost of the casement windows vs the 4'x4' sliding windows, I was planning on increasing the width of the opening. The current windows are very small. By increasing the height of the window to 4', it will bring the bottom of the window to within 44" of the floor. How can I install a new lentil beam?

What is the width of the current window?

The offset in cost between the material cost of a slider and a casement will easily be absorbed by the added labor or putting in a new lentil.

This does not account for the added expense of labor if you disturb and damage any brick.

Also, I think it is worth noting that depending on the type of 2-Lite slider that you go with, the 48" rough opening will probably not give you the net clear 20" code requires.

You will loose some of the width opening to frame material on either side of the actual window and no 2-Lite slider opens 100%.

To be safe, you should consider a 2-Lite slider that is closer to 54" wide.

Now you have a pretty large 2-Lite slider requirement who's height will also be dictated by code.

Typically Casement windows are about $50 more expensive per unit than a comparably sized 2-Lite.