You should be able to turn off the lock screen security somewhere in Settings>Security>Screen Lock and then change it to none or just a simple slide to unlock or whatever you want. This is how you get to it on my S3, but yours should be similar no matter what phone you have.
To fix your other issue, also in the Security tab on my phone, there should be a tab called "Device Administrators." When you go into this tab, it allows you to check and uncheck which apps have access. If you uncheck the app that is preventing you from changing this, it might solve your problem.