Yes you will have no problem at all. It is safe to use speakers rated higher than your amplifier but not the other way around. Essentially lower ohms means less resistance which makes the amp have to work harder to give the speaker the power it requires.
The only thing you may notice is that with higher ohm speakers you need to turn the volume knob higher to get the same relative volume.
Also, if you wire two speakers in parallel (meaning to the same output jacks) it will lower the total impedance. You can find an online calculator to check to make sure the impedance doesn't go below 4ohms.