You can temporarily deactivate Cloudflare by going to the Overview app and activating Pause Website under the Advanced section:
Pausing Cloudflare will cause your origin IP address to be returned by Cloudflare's nameservers, sending traffic directly to it rather than through Cloudflare's reverse proxy. No Cloudflare services such as SSL or WAF will be enabled on that domain or subdomains while the site is paused. An alternative to pausing Cloudflare would be to use Development Mode, which will only bypass Cloudflare's cache, but still provide other services such as SSL.
We do not recommend changing away your name servers as that can have a delay of several hours whereas pausing Cloudflare takes 5 minutes or less to temporarily resolve whatever issue you may be having.