7 is narrower spaced 6 wider, overall width is similar... (8 is 7+1 with similar narrow spacing) and should be a simple swap , (9 is even narrower spaced)
may need 1 freewheel remover to take that off and a different one for the new one.
so better to have the bike shop do it , rather than a specialty tool you use once.
+ a new chain of course..
...
