Editing the custom spelling dictionaries in Excel is a relatively simple process, but one that can be quite time consuming if you have a lot of words to add or remove. The first thing you need to do is open up the Excel application and then click on the 'File' tab at the top left of the screen. From here, select 'Options' and then choose 'Proofing' from the list of available options on the left hand side. Once you're in the Proofing options menu, click on the 'Custom Dictionaries' button near the bottom.
This will open up a new window called 'Custom Dictionaries'. Here, you'll see a list of all the custom dictionaries that are currently active in Excel. If you want to edit an existing dictionary, simply click on it and then press the 'Edit Word List' button. If you want to create a new dictionary, press the 'New' button and give your dictionary a name.
Once you've selected the dictionary you want to edit, another window will pop up with a list of all the words currently in that dictionary. To add a new word, simply type it into the 'Add to Dictionary' field at the bottom and then press the 'Add' button. To remove a word, select it from the list and then press the 'Remove' button. Once you're done adding or removing words, press the 'OK' button to save your changes.