Customizing Lastform URL
To avoid conflicts with other plugins, your form default slug is "lastform", but you can change it. Here is how go to "Forms / Settings → Lastform → Form URL Slug":
Once you change for, let's say, "ourforms", just click "Update Settings".
WARNING: Flush your Rewrite Rules!
Once you click "Update Settings", you need to flush your Rewrite Rules after changing it.
To do this, you just need to go to the "Settings → Permalinks" page and click "Save Changes" to flush the rules: