How to remove Crash Dump Files under Windows 7
Disk Cleanup, built-in with Windows, can perform this task for you; you must be administrator to perform this task. Another way is to just remove the files you have found through WinDirStat. As long as you remove the *.mdmp files and no other important system files...
You might want to examine your event logs though to see why so many crashes have occured! ;-)