I open the "Site Settings" later "Site Permissions" And i give some users Edit,Approve permissions. but their permission levels are not updated. They cannot edit the page. How can i solve this?
if the page as unique permissions, then giving permission on site won't help. So give permission on particular page .
click on share and give permission to that person. then he will be able to see and edit that page. give minimum design permission. To edit the page design permission is required.in on-premise servers share option will be like manage permissions or shared with.
Try giving them "Design" level permissions. This should solve the issue.