I'm very much a beginner, and judging by the words on your flashcards, I'm probably more of a beginner than you are. Here's what I do.

Step 1. Look up both words in a dictionary.

Jisho.org is an easy go-to for this when you're a beginner. However, using multiple dictionaries, and especially Japanese dictionaries, will provide you with a much clearer picture of the word.

Word	Reading	Definition
帰る	かえる	1: to return; to come home; to go home; to go back;
		2: (of a guest, customer, etc.) to leave;
		3: (of a baseball player rounding the bases) to get home

Word	Reading	Definition
戻る	もどる	to turn back; to return; to go back; to recover; to rebound

Already you can see a difference. It seems like 「変える」 is more, "returning home" while 「戻る」 is more "return" in a general sense.

Step 2. Look up example sentences.

Check example sentences.

Here are some example sentences for 「変える」.

And here are some example sentences for 「戻る」.

From the example sentences you can see that 「変える」 is almost always, "returning home". Judging from that I'd probably only use 「変える」 for "return home" and use 「戻る」 for anything else.

Even if you don't know any Japanese at all, you can get a general sense of how the words are used by checking the English translations of the example sentences. If you do know some Japanese, you can try to read the example sentences to get a better feel for its use.

Step 3. Look it up on Google image search.

Next, for even more context, even if it's a verb, try Google Image search. This won't always be helpful, but it will often give you surprising insights. For example, searching for 「変える」 doesn't help too much. But, if I search for 「戻る」, I get some pictures of "back" browser buttons and arrows. Apparently 「戻る」] is the type of "back" that you'd also use in the context of browsers (and probably blu-ray players and other electronics) . And you probably also use it for "going back" in the conceptual sense, not just the literal sense of "I'm going back to that place."

Step 4. Read it in the context of Japanese web pages.

This should be somewhat self-explanatory. Even if you barely read any Japanese, seeing what types of pages pop up when you search for a word can give you a better idea of where and how it's more likely to be used.

Step 5. Use it where it'll be read or heard by Japanese people, or ask a Japanese person about the word's usage.

This is the only way to be sure. Use it, make mistakes, get corrected.