What kind of grass is it? Have you not been cutting it back for 7 years?

The best thing to do is cut them right down to almost ground level in early spring before they start to grow, and you should do this every year. If they've grown too thick, you might need to dig them up and divide them. This isn't for the faint of heart. You need a strong back and shovel and an ax to split mature grasses that are as big as you describe.

If you've never cut them down before, try doing just that this spring, and see if that helps them to look better.

Here is a link that might be useful: care of ornamental grasses

I'm going to disagree slightly :-) Not all grasses need to be cut back every year. A number of evergreen grasses never require being cut back and some will resent that sort of attention. True pampas grass - Cortaderia selloana - is fully evergreen in warmer climates and does not require this type of attention except when the plant just gets too large for the location or becomes very ratty looking due to weather (snow loads, high winds, etc.).

But all of this is speculation until the OP provides feedback on the type of grass he has. Then we can offer specific pruning/shearing advice for that type of grass.