Hi camilafromcambridge,
It appears you are unable to access updates in the Mac App Store. You may want to try signing out of the store, and signing back in. I've included an article which explains how to do so. I've also linked to an article on how to change your Apple ID password if necessary:
Mac App Store: Sign in and out
To make purchases, you need to sign in using an Apple ID.
If you already have an iTunes Store account or another Apple account, you can use that Apple ID. If you don’t already have an Apple ID, you can create one in App Store.
- Choose Store > Sign In, or click Sign In in the Quick Links section.
The Quick Links section is located in the right part of the window shown when you click Featured, Top Charts, or Categories in the toolbar.
- Enter your Apple ID and password, and then click Sign In.
- Do one of the following:
Choose Store > Create Account.
Choose Store > Sign In or click Sign In in the Quick Links section, and then click Create Apple ID.
The Quick Links section is located in the right part of the window shown when you click Featured, Top Charts, or Categories in the toolbar.
- Follow the onscreen instructions to create a new Apple ID.
- Choose Store > Sign In or click Sign In in the Quick Links section.
- Enter the new Apple ID and password, and then click Sign In.
When you are finished using App Store, you can sign out to prevent anyone who can access your computer from making purchases using your Apple ID.
Choose Store > Sign Out.
Choose Store > View My Account, or click Welcome in the Quick Links section.
The Quick Links section is located in the right part of the window shown when you click Featured, Top Charts, or Categories in the toolbar.
If you forgot your Apple ID password - Apple Support
Thank you for contributing to Apple Support Communities.
Take care,
Bobby_D