is there anyway I can access my webpage to change some detail without notifying my web designer (long story!)?

Question

I do not have his password to access the page but I do have proof of my ownership of site and it is registered in my name

Answer 1

Convince the host to give you the password. Call their customer support. Should be simple enough.

Answer 2

then u would need to speak the the hosting company, but they will proberly wipe all the pages since they are not going to remove it for you.