If want to use shift to LM or any other similar superior performance oil, then YES its better to use engine flush as it drains out more than 95% particles/contents of the old oils.
Better oil choice for Lancer can be
LM 5/40 Synthoil Hi-Tech. SCI 8~10K.
Kixx PAO 5/40. SCI 8~10K.
ZIC XQ 5/40. SCI 8~10K.
Valvoline 5/40. SCI 8~10K.
Kixx PAO Neo 5/30. SCI ~6K.
PTT Performa 5/40. SCI ~8K.
Total 9000 5/30. SCI ~6K.
Ptt, LM & kixx, also has 0/40 oil in fully synthetic. If can find them, then use this oil for sure. Because general specifications of this 0/40 & 5/40 is almost same, price is also same, but performance wise 0/40 is slightly ahead than 5/40.
Change both filters with oil change & after 3~4K too.