You cannot select and delete an inflection feature from the Inflection Features field. Instead, do the following:
In the Navigation Pane, click Lexicon, and then click Lexicon Edit.
In the Entries pane, click the entry that has the feature you will delete.
In the Entry pane, if you cannot see the Inflection Features field under the Grammatical Info Details field, show hidden fields.
Click the Inflection Features field, and then click the ellipsis button that appears.
The Choose Inflection Features dialog box.
Choose None of the Above or a different inflection feature.
Click OK.
It is strongly recommended that you contact a FLEx consultant before you overtly add or edit features or feature types. If these are not handled correctly, the parser may not analyze many of your word forms.
About Inflection Features and Feature Types