如果文件的编号大于X，则如何删除不可预测的文件数

I have a number of files in directories which are numbered as file_1.txt, file_2.txt, file_3.txt and so on. I would like to delete any files with a number above, for example, 5 (so deleting file_6.txt, file_7.txt and so on). I do not know how many of these files there are in each directory, or if there even are that many files. These numbers do not correspond to how recently the files were last accessed. I have a number of files in directories which a