At least, you're already at 7.0. My server is stuck at 5.6, and there's no word on when it will be updated. They tell me it's "in the works", but won't say when. Considering that everything less than 7.1 is out of support, this is absurd.
If you are getting "deprecated" warnings, upgrading PHP is only going to make it worse. Your software (such as Joomla) needs to be upgraded to match the PHP you have now (7.0). Joomla is telling you to go to 7.1 because that's what is supported, not because it will get rid of "deprecated" errors. Simply upgrading to 7.1 is only going to make the current errors worse.