One cannot UpVote without spending Steem. That's all part of the grand design. Spend what you can / want to spend, to support those Steemers or posts that you want to support / encourage.

At the same time, the system will constantly generate new Steem, and distribute that new Steem to the Steemians. Basically, it will refill your tank – automatically. A refill will take a few hours or a few days, depending on how much Steem you have recently spent.

Here's a link to a great page – https://steemnow.com ... Under "SETTINGS," input your Steemit Username, and click "ENTER", and your relevant stats will appear.

In the green bar, you will see your current "VOTING POWER." If it is less than 100%, it will tell you how long you must wait for your "Tank" to be refilled with Steem. If you do not spend any Steem in upvoting, it will be refilled in that time frame.

Of course, if you spend some Steem upvoting, the "refill" time will be further extended.

Hope this helps. (It took me a while to learn the, too.)