A Lawrence city councilor will try to unseat William Lantigua, the city’s embattled mayor, in the election later this year. Councilor Dan Rivera is scheduled to announce his candidacy for mayor Wednesday, his campaign said. The statement said Rivera will focus in part on “rehabilitating Lawrence’s image across the state.” Lantigua, a Democrat, has denied allegations of ­political corruption in his administration. Two subordinates have been indicted on criminal charges, but Lantigua has not been charged with any wrongdoing.