How do I correct a spelling of a name in the 1950 census?

Len....  the 1950 census is a historical document, warts and all.  The original sheets were destroyed in the 1960s, and all we have today is the scanned media.  You can't "correct" the document.  I am assuming that what is "misspelled" is on the actual census sheet and not on an incorrect transcription.  You can, however, augment name indexes that were transcribed off of the 1950 films.  For example, at the NARA site: https://1950census.archives.gov/, once you get to the image that has your target, you will see "Help Us Transcribe Names" where you can add the correct name to your grandfather's line.  What will happen is that both the original translation (done by OCR computer algorithm) and your corrected name will be both searchable leading to the same record.

 lenczad