If the owner is quitting, why did they not make you owner ? A lot of permissions belong only to the clan owner and cannot be passed on even to a deputy. If the owner really is quitting, getting him to make you owner now will be for the best. Being dept with an inactive owner wont be easy. As far as name changing goes, only the owner may change the name.
I see you've posted in the Inactive Clan Leaders thread as well, so I'll try to answer all of the questions you asked.
Based on your current Clan Owner's RuneMetrics profile, he has gained 183,882 xp (as of right now) during this month. Given this information, your clan does not qualify for the removal of an inactive Owner. He would need to have not logged in to the game for a full year in order to qualify.
Also, (if I remember correctly) when a Clan Owner leaves a clan (or demotes him/herself), the Deputy who has been a member of the clan longest is the one who becomes the next Clan Owner when the position becomes empty, not the first name in alphabetical order. This is why it is recommended that all other Deputies are temporarily demoted to ensure the position goes to the correct person during a change of ownership.
Unfortunately, you will need to get in contact with your Clan Owner and have him pass on the rank to the desired person as there is nothing Jagex can do for your clan in this case. He will need to demote himself to a rank of Admin or lower in order to do this.
As for changing your clan's name, the Clan Owner is the only one who is able to change it. You will need to sort out the ownership issue before dealing with that.
If you're open to this, there is the option of starting a new clan to solve the issues you're having.
Hope you're able to get this sorted.
By the way, for future reference, it's always a good idea to create a new thread on the forums to ask a question rather than dig up an old thread from August 2017 that had a different question, albeit the same topic, and was answered over one year ago. If you don't want to make a new thread in this forum section, you can use the ? Clan Help ¿ thread that is pinned at the top. ~ Sicariu